USPL-FSO lasercom point-to-point and point-to-multipoint optical wireless communication

ABSTRACT

Enhancements in optical beam propagation performance can be realized through the utilization of ultra-short pulse laser (USPL) sources for laser transmit platforms, which are can be used throughout the telecommunication network infrastructure fabric. One or more of the described and illustrated features of USPL free space-optical (USPL-FSO) laser communications can be used in improving optical propagation through the atmosphere, for example by mitigating optical attenuation and scintillation effects, thereby enhancing effective system availability as well as link budget considerations, as evidenced through experimental studies and theoretical calculations between USPL and fog related atmospheric events.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application claims priority under 35 U.S.C. §119(e) to U.S.provisional patent application No. 61/584,666 filed on Jan. 9, 2012, thedisclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The subject matter described herein relates to free-space optical (FSO)wireless communications, and more particularly, to enhanced opticaltransport efficiencies that can be realized for wavelength propagationusing ultra-short-pulse-laser (USPL) sources for beam propagationthrough optically impaired atmospheric conditions due to conditions thatcan include without limitation fog, atmospheric beam wander,scintillation effects, and the like.

BACKGROUND

Explosive growth in demand for telecommunication services, from both theprivate as well as commercial sectors, has placed an unprecedentedstrain upon currently available telecommunications networks. Withoutalternative network delivery technologies and topologies, overalleffective network speed is likely to be reduced while occurrences ofbottlenecks within networks will become increasingly frequent.

Bi-directional, free-space optical (FSO) communications networks can,where feasible, provide a useful alternative to microwave links, wire,or cable system applications. Such networks can be transparent tocurrent as well as future network architectures due to sharing of commontechnological platforms with fiber optic transmission systems, thebackbone of many present day telecommunication systems. FSOcommunication systems can generally share common fiber-optic components,and commercial optical components can often utilized for bothapplications. The primary difference in free-space optical data linksystems is that the medium of propagation is the atmosphere rather thanoptical fiber.

Utilizing current state-of-the art fiber-optic components, free-spaceoptical data links can be fully integrated into current short-haul andlong-haul high-speed optical networks. Free-space data links can fullyattain current synchronous optical networking (SONET) systemarchitectures, such as for example SONET OC-48 architectures utilizingcurrent 1550 nm technology platforms. Additionally, such systems can bescaled to higher data rates and configurations. Optical data linksystems can benefit from operating in an unregulated segment of theelectro-magnetic spectrum. Unlike the microwave and RF spectrum, opticaldata links can generally require no special leasing fees or tariffs tobe issued. Additionally, because of the operating wavelength of thesystem, issues related to eye safety can generally be minimized.Furthermore, no special precautions or permits are typically requiredoperating a free-space data link related to territorial right-of-ways.Expenses related to plowing and trenching of fixed cabled systems canalso be avoided.

More recently, FSO communication technology has leveraged commercialadvancements made within the 1550 nm optical transmission band. Erbiumfiber doped amplifier (EFDA) technology has been incorporated withinsystem design configuration for enhancing the overall effective opticalbudget of transport budgets and thereby extending the reach of transportsystems over the air.

High power optical amplifiers are useful for terrestrial free-spacetransmission as well as fiber optic systems. Repeater distances havebeen extended in terrestrial and submarine fiber systems and densewavelength division multiplexing (DWDM) transmission architectures havebeen introduced. With the advent of high power Er/Yb optical amplifiers,similar advances as seen in fiber optic transmission have also beenrealized in optical wireless and free-space laser communicationssystems. Experimental transmission results for a single-channel 1550 nmfree-space optical data-link operating at 2.5 Gbps over a 2.4 kmtransmission span have been reported, as have results for a four-channel1550 nm wavelength division multiplexing (WDM) free-space optical datalink operating at 10 Gbps over a 4.4 km transmission distance.

SUMMARY

In some implementations of the current subject matter, an opticalcommunication apparatus and a method for operating the same are providedfor the generation and transmission of a modulated signal.

In one aspect, the optical communication apparatus includes anultra-short-pulse-laser (USPL) source that generates a beam of lightpulses. Each lights pulse has a duration of approximately 1 nanosecondor shorter. The optical communication apparatus further includes amodulation element that applies a modulation signal to the beamgenerated by the USPL source to generate a modulated optical signal. Themodulation signal carries data for transmission to a second opticalcommunication apparatus. The optical communication apparatus furtherincludes an optical transceiver that receives the modulated opticalsignal and transmits the modulated optical signal for receipt by thesecond optical communication apparatus.

In an interrelated aspect, a method includes generating a beam of lightpulses. Each of these light pulses has a duration of approximately 1nanosecond or shorter. The method further includes applying modulationsignal to the beam to generate a modulated optical signal. Themodulation signal carries data for transmission to a second opticalcommunication apparatus. The method further includes receiving themodulated optical signal at an optical transceiver, and transmitting,using the optical transceiver, the modulated optical signal for receiptby the second optical communication apparatus.

In another interrelated aspect, a method includes generating first andsecond beams comprising light pulses; applying a first modulation signalto the first beam to generate a first modulated optical signal and asecond modulation signal to the second beam to generate a secondmodulated optical signal; adjusting a first polarization state of thefirst modulated optical signal; multiplexing the first modulated opticalsignal having the adjusted first polarization state with the secondmodulated signal; and transmitting the multiplexed first modulatedoptical signal having the adjusted first polarization state with thesecond modulated signal by an optical transceiver for receipt by asecond optical communication apparatus.

In an interrelated aspect, an optical communication apparatus includes afirst laser source that generates a first beam comprising light pulsesand a second laser source that generate a second beam comprising lightpulses. A first modulation element applies a first modulation signal tothe first beam to generate a first modulated optical signal. The firstmodulation signal carries first data for transmission to a remoteoptical communication apparatus. A second modulation element applies asecond modulation signal to the second beam to generate a secondmodulated optical signal. The second modulation signal carries seconddata for transmission to the remote optical communication apparatus. Afirst polarization component adjusts a first polarization state of thefirst modulated optical signal. A polarization dependent multiplexercomponent multiplexes the first modulated optical signal having theadjusted first polarization state with the second modulated signal. Anoptical transceiver receives the multiplexed optical signal firstmodulated optical signal with the adjusted first polarization statehaving the second modulated signal and transmits the multiplexed firstmodulated optical signal having the adjusted first polarization statewith the second modulated signal for receipt by the second opticalcommunication apparatus.

In further variations, one or more of the following additional featurescan be included in any feasible combination. With regard to the opticalcommunication apparatus, the modulation element can include at least oneof a direct modulation element, an indirect modulation element, and anexternal modulation element. The external modulation element can beexternal to the USPL source.

In some variations, the duration of each light pulse can be less thanapproximately a picosecond. In other variations, the duration of eachlight pulse can be less than approximately a femtosecond. In still othervariations, the duration of each light pulse can be less thanapproximately an attosecond.

Alternatively or in addition, the optical communication apparatus canfurther include an optical multiplexer that multiplexes more than onecommunication channel into the beam.

In some variations, the optical communication apparatus can furtherinclude an optical amplifier disposed between the USPL source and theoptical transceiver. The optical amplifier can increase an output powerof the modulated optical signal transmitted by the optical transceiver.In some variations, the optical amplifier can include at least one of anoptical pre-amplifier, a semi-conductor optical amplifier, anerbium-doped fiber amplifiers, and an erbium-ytterbium doped fiberamplifier.

In other variations, the optical communication apparatus can furtherinclude a second USPL source that supplies a second beam of light pulsesto the optical transceiver. The second USPL source can serve as atracking and alignment beacon to determine or verify a target point forthe transmitted modulated optical signal at the second opticalcommunication apparatus.

In yet other variations, a tracking and alignment beacon signal can begenerated within the modulated optical signal. The tracking andalignment beacon signal can be used to determine or verify a targetpoint for the transmitted modulated optical signal at the second opticalcommunication apparatus.

In still other variations, the optical communication apparatus canfurther include a polarization dependent multiplexer component thatmultiplexes optical signals of differing polarity before transmission ofthe modulated optical signal to the second optical communicationapparatus.

In some variations, the optical communication apparatus can furtherinclude a polarization dependent de-multiplexer component thatde-multiplexes optical signals of differing polarity received as asecond modulated optical signal from the second optical communicationapparatus. The de-multiplexed optical signals can each be interfaced toa different optical network for network usage.

In some implementations of the current subject matter, a remote sensingapparatus and a method for operating the same are provided. In oneaspect, a method includes generating, using a USPL source, a beam oflight pulses each having a duration of approximately 1 nanosecond orshorter; transmitting the beam of light pulses toward a targetatmospheric region via an optical transceiver; and analyzing opticalinformation received at the optical transceiver as a result of opticalbackscattering of the beam of light pulses from one or more objects inthe target atmospheric region.

In an interrelated aspect, a remote sensing apparatus includes anultra-short-pulse-laser (USPL) source that generates a beam of lightpulses each having a duration of approximately 1 of nanosecond orshorter; an optical transceiver that transmits the beam of light pulsestoward a target atmospheric region; and detection circuitry foranalyzing optical information received at the remote sensing apparatusas a result of optical backscattering from one or more objects in thetarget atmospheric region. The remote sensing apparatus can optionallyinclude a spectrographic analysis component for analyzing spectroscopicinformation extracted from the optical information received at theremote sensing apparatus.

Implementations of the current subject matter can include, but are notlimited to, systems and methods including one or more features asdescribed herein as well as articles that comprise a tangibly embodiedmachine-readable medium operable to cause one or more machines (e.g.,computers, etc.) to result in operations described herein. Similarly,computer systems are also described that may include one or moreprocessors and one or more memories coupled to the one or moreprocessors. A memory, which can include a computer-readable storagemedium, may include, encode, store, or the like one or more programsthat cause one or more processors to perform one or more of theoperations described herein. Computer implemented methods consistentwith one or more implementations of the current subject matter can beimplemented by one or more data processors residing in a singlecomputing system or multiple computing systems. Such multiple computingsystems can be connected and can exchange data and/or commands or otherinstructions or the like via one or more connections, including but notlimited to a connection over a network (e.g. the Internet, a wirelesswide area network, a local area network, a wide area network, a wirednetwork, or the like), via a direct connection between one or more ofthe multiple computing systems, etc.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims. While certain features of the currently disclosed subject matterare described for illustrative purposes in relation to an enterpriseresource software system or other business software solution orarchitecture, it should be readily understood that such features are notintended to be limiting. The claims that follow this disclosure areintended to define the scope of the protected subject matter.

DESCRIPTIONS OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, show certain aspects of the subject matterdisclosed herein and, together with the description, help explain someof the principles associated with the disclosed implementations. In thedrawings,

FIG. 1 depicts an example of an optical communications platformincluding free-space coupling of a USPL source as an optical source fortransport to a remote optical receive terminal;

FIG. 2 depicts an example of an optical communications platformincluding fiber coupling of a USPL source as an optical source fortransport to a remote optical receive terminal;

FIG. 3 depicts an example of an optical communications platformincluding fiber coupling of a USPL source to an external modulator fortransport to a remote optical receive terminal;

FIG. 4 depicts an example of an optical communications platformincluding fiber coupling of a USPL source to an external modulatorthrough a fiber medium for transport to a remote optical receiveterminal;

FIG. 5 depicts an example of a transmitting and or receiving elements,which can be of a type from either the Hyperbolic Mirror FabricationTechniques or conventional Newtonian designs;

FIG. 6 depicts an example of an optical fiber amplifier elementidentified and used to increase enhancing optical transmit launch powerfor transport to a remote optical receive terminal;

FIG. 7 depicts an example of a USPL laser device that is fiber coupledto an external modulator for transport, in a point-to-pointconfiguration for transport to a remote optical receive terminal;

FIG. 8 depicts an example of a USPL laser device that is fiber coupledto an external modulator for transport, in a point-to-Multi-pointconfiguration;

FIG. 9 depicts an example of use of USPL sources acting as tracking andalignment (pointing) beacon sources;

FIG. 10 depicts an example of a USPL laser sources polarizationmultiplexed onto a transmitted optical signal, to provide PolarizationMultiplex USP-FSO (PM-USP-FSO) functionality;

FIG. 11A and FIG. 11B respectively depict examples of USPL-FSOtransceivers utilized for use in line-of-sight and non-line-of-sightlasercom applications;

FIG. 12 depicts an example of light propagated forward beingbackscattered by interaction with air-borne particulates that are thesubject of investigation;

FIG. 13 depicts an example of USPL laser sources as optics receptiontechniques to improve detection sensitivity consistent with animplementation of the current subject matter; USPL laser sources as wellas optical reception techniques to improve detection sensitivity.

FIG. 14 depicts an example of a USPL-FSO transceiver utilized andoperated across the 1.3 to 1.6 micron wavelength range as a range-finderand spotting apparatus for the purposes of target identification;

FIG. 15 depicts an example of a USPL pulse multiplier device consistentwith implementations of the current subject matter;

FIG. 16 depicts another example of a device for generation of high pulserate USPL optical streams consistent with implementations of the currentsubject matter;

FIG. 17 depicts another example of an optical device to a generate aUSPL RZ data stream from a conventional transmission networking element;

FIG. 18 depicts an example of a implementing a USPL pulse multiplierdevice for generation of 10×TDM type signals system to give a 100 Gbpsoutput;

FIG. 19 depicts an example of a implementing another type of USPL pulsemultiplier device for extending the pulse repetition rate for use inhigh capacity networks;

FIG. 20 depicts an example of a implementing another type of USPL pulsemultiplier device for extending the pulse repetition rate for use inhigh capacity networks;

FIG. 21 depicts examples of active mode-locked linear fiber lasers withfeedback regenerative systems: fiber reflector (FR), wavelength-divisionmultiplexer (WDM), Erbium-doped fiber (EDF), optical coupler (OC),photo-detector (PD), phase-locked loop (PLL), and Mach-Zender Modulator(MZM);

FIG. 22 and FIG. 23 depict examples of passive mode-locked linear fiberlasers using a carbon nano-tubes saturable absorber: fiber reflector(FR), wavelength-division multiplexer (WDM), Erbium-doped fiber (EDF),optical coupler (OC), and saturable absorber (SA);

FIG. 24 depicts an example of a time-delay stabilization mechanism:optical coupler (OCin, OCout), photo-detector (PDin, PDout), high-passfilter (HPF), low-pass filter (LPF), phase-locked loop (PLL),phase-comparator (PC), frequency-divider (1/N), clock-data recoverysystem (CDR), piezoelectric actuator (PZ1 . . . PZN), summing op amp,for use in stabilizing the optical pulse to pulse relationship producedfrom the USPL source;

FIG. 25A and FIG. 25B respectively include a schematic diagram and agraph relating to an example of a controlling mechanism to stabilize theoutput frequency of TDM sources utilizing an idealized PZ actuator;

FIG. 26 depicts an example of a Time-Domain Multiplexing (TDM) where theTDM multiplexes a pulse train using parallel time delay channels, havingthe delay channels to be “consistent” relative to each another (Becausethe frequency of an output multiplexed pulse train is ideally asinsensitive as possible to environmental changes, a feedback loopcontrol system can correct the delay units for any fluctuations whichcompromise the stability of the output rep rate, and feedback can beprovides through interconnection to a Neural Network);

FIG. 27 depicts an example of use of fiber based collimators along withPiezoelectric transducers for controlling individual MFC circuits;

FIG. 28 depicts an example of timing of the TDM chip from the USPLmodulation source to provide a Terabit/second (or faster) with aMultiplier Photonic chip;

FIG. 29 depicts an example of timing of the TDM chip from the USPLmodulation source to provide a Terabit/second (or faster) with aMultiplier Photonic chip operating in a WDM configuration;

FIG. 30 depicts an example of construction of a computer assistedsystem, which can control the pulse width of an all-fiber mode-lockedlaser using recursive linear polarization adjustments with simultaneousstabilization of the cavity's repetition rate using a synchronousself-regenerative mechanism and can also offer tunability of therepetition rate, and pulse width;

FIG. 31 depicts an example of a modified pulse interleaving scheme, by apulse multiplication technique, in which the lower repetition rate pulsetrain of a well-characterized, well-mode locked laser can be coupledinto an integrated-optical directional coupler, where a well-determinedfraction of the pulse is tapped off and “re-circulated” in an opticalloop with an optical delay equal to the desired inter-pulse spacing inthe output pulse train, and re-coupled to the output of the directionalcoupler;

FIG. 32 is a process flow chart illustrating features of a methodconsistent with implementations of the current subject matter;

FIG. 33 is another process flow chart illustrating features of a methodconsistent with implementations of the current subject matter; and

FIG. 34 is another process flow chart illustrating features of a methodconsistent with implementations of the current subject matter.

DETAILED DESCRIPTION

One or more implementations of the current subject matter can provideimproved optical propagation efficiencies for free-space opticalwireless optical communication systems that operate within the C-bandwavelength spectrum. These efficiencies can be realized in reducedoptical attenuation coefficient reduction along with significantlyimproved scintillation performance characteristics when compared tocurrent FSO communication systems operating within the 1550 nm C-band.

Typically, use of FSO along with high-power optical amplificationtechniques can generally realize only marginal increases in opticalbudget and system availability, especially during fog related events,during which optical attenuation within the transmitted band can rise to100 dB/km and higher. A common limitation to system performance forcurrently available 1550 nm FSO systems, and also to systems operatingat shorter optical operating wavelengths, is wavelength susceptibilityto attenuation due to fog related effects. Such attenuation can becaused by both geometric and Mie scattering mechanisms. Systemavailability for FSO transmission networks can be severely reduced orimpaired due to a large optical loss coefficient due to fog relatedevents, in which optical losses due to atmospheric absorption can exceed100 dB/km for dense fog conditions. In such cases, system availabilityconsiderations can be compromised even for links of only severalkilometers in length. Currently available commercial FSO transportsystems can be limited for high availability, high capacity long rangeoperation. Additionally, current state-of-the-art free-space opticalcommunications systems generally require large amounts of optical launchpower to overcome gradual reductions in line-of-sight visibility throughaerosol and fog related atmospheric events. Such systems can in somecases become totally inoperable and therefore unavailable ascommunication links during mild or heavy fog events, thereby resultingin link outages.

Recent advances in alternate FSO laser transmission sources within the1550 nm transmission window have been reported in which USPL technologyhas been successfully demonstrated as a potential replacement technologyfor currently used 1550 nm optical FSO technology. USPL laser sourcepulse propagation tends to be less susceptible to interaction with fogparticulates. Accordingly, optical attenuation effects can generally bemore readily mitigated, which can result in reduced optical attenuationand improved link availability and overall system performance.

Current state-of-the-art free-space optical communications systemsgenerally utilize optical tracking to maintain optical co-alignmentbetween optical transceiver platforms. Such optical tracking can bethereby limited to the same extent as that of the data carrying channelsfor in-band transmission channels. As atmospheric conditionsdeteriorate, tracking and steering beacons can become ineffective inmaintaining co-alignment between transceivers. In instance in whichincreasing optical transport densities are ineffective to overcomereductions in line-of-sight visibility through aerosol and fog relatedatmospheric events, such approaches can become totally inoperable duringmild or heavy fog events, thereby leading to link outages. Also, duringhigh scintillation conditions, signal wander and speckle effects canseverely limit both signal propagation and beacon tracking signalsbetween terminals along the optical data link.

Conventional free-space optical beam propagation is typically affectedby atmospheric absorption from particulates and aerosols interactingwith the optical beam over the link span. These phenomena can have acumulative effect upon the overall received power level of the signaland can also cause fluctuations in the detected optical power level dueto temporal instabilities of the attenuation mechanisms within the beampath. The transmitted optical power at a specific distance is given byBeer's Law, which can be expressed asT[R]=P[R]/P[0]=e ^(−σ*R)  (1)

where T[R] is the transmittance at range R, P[R] is the link power atrange R, P[0] is the initial launched data link optical power, and σ isthe attenuation coefficient per unit length. The attenuation coefficientper unit length, σ, can be the overall atmospheric attenuationcoefficient, which can be composed of four variables, for example asfollows:σ=α_(m)+α_(a)+α_(m)+α_(a)  (2)

where α_(m), α_(a), α_(m), and α_(a) are the molecular absorption,aerosol absorption, and Rayleigh and Mie scattering coefficients,respectively.

When the size of atmospheric particles approaches the wavelength of thepropagating beam, Mie scattering typically dominates the totalattenuation coefficient. The Mie scattering coefficient can be expressedas a function of atmospheric visibility and wavelength, and can be givenby the following expression:σ_(a)=˜=σ=[3.91/V](V/550)^(−q)  (3)

where V is the visibility (km), λ is the wavelength (nm), and q=sizedistribution of scattering particulates and takes on values for variousvisibility conditions. The value q in the above equation takes on thefollowing values under various visibility condition: q=1.6 for highvisibility conditions (e.g. V>approximately 50 km); q=1.3 for averagevisibility (e.g. approximately 6<V<approximately 50 km); q=0.585V^(1/3)for low visibility (e.g. V<approximately 6 km); q=0.16 V+0.34 for hazevisibility (e.g. approximately 1 km<V<approximately 6 km); q=V−0.5 formist visibility (e.g. approximately 0.5 km<V<approximately 1 km); andq=0 for fog visibility (e.g. V<approximately 0.5 km).

Because of the shorter transmission wavelengths of 1550 nm free-spacelinks, these signals can be more susceptible to atmospheric effects whencompared to RF and microwave communications. Atmospheric effects candeteriorate free-space laser link transmission by either or both ofoverall reduction in detected optical power level due to atmosphericattenuation and random optical power fluctuations in the received signalresulting from beam deformation, scintillation effects, and beam wander.

As a conventional free-space optical laser beam propagates through theatmosphere, it generally experiences deterioration and deformation ofits wave-front. These degradation modes are caused from small scale,randomly localized changes in the atmospheric index of refraction, whichresult in beam wander and distortion of the wave-front and scintillationeffects. Temperature gradients between ground and atmospheric conditionslead to atmospheric turbulence, which in turn lead to small scale,localized random pockets of varying indices of refraction. Whenscintillation cell size is smaller than the diameter of the laser beamdiameter, the optical beam will experience distortion, and a non-uniformoptical intensity across the wave-front will be observed. This effect iscalled scintillation. If the size of the interference cell is largerthan the laser beam diameter then the bean will randomly wander offcourse of the site path. The mixing of scintillation and beam wander canlead to fluctuations in overall signal stability. Therefore, the beamcan experience a propagation path that is non-homogeneous both spatiallyand temporally, which can cause the beam to propagate in a randommanner. These effects generally add together to produce an overall noisecomponent to the received optical signal.

Scintillation effects can be strongly dependent upon the concurrentvisibility at the link sites, and also vary with link range.Experimental studies indicate that USPL beam propagation can experienceless susceptibility to the effects of scintillation and beam wanderphenomena. Accordingly, USPL-FSO laser communication sources can be auseful replacement technology within a FSO transport platform for notonly data transport but also for use as optical beacon applications foruse in pointing-and-tracking applications, at least because of therelative resistance of such beams to wander and to be affected byatmospheric scintillation. Such benefits can be realized throughenhanced visibility performance as compared to conventional FSOpropagation techniques as well as improved scintillation and beam wanderperformance.

Attenuation through heavy fog conditions can limit signal propagationusing conventional free-space optical schemes, regardless of opticallaunch power densities. USPL laser pulses can occupy a much smallerspatial dimension. For example, a 100 femtosecond (fs) pulse generallyoccupies 30 microns in a dimension along the axis of propagation of thelight. Thus, interaction of the pulse with the droplets of water thatconstitute fog and clouds, which typically have diameters in the rangeof tens of microns, can be reduced by one or more orders of magnitude,and in some examples by a factor of 1000 or more while carrying the sameamount of energy, compared to longer-pulse radiation from conventionallaser sources. The result of this effect can be that laser pulses on theorder of 100 fs do not excite power scavenging whispering-galleryphysics in the water droplets to the same extent as longer pulses. Suchphenomena can generally scale exponentially for continuous wave (CW)lasers, especially during heavy fog. Benefits of USPL laser sourcesconsistent with implementations of the current subject matter can resultin up to 8 times the visibility of traditional sources.

FSO transport systems can typically utilize a transmitting telescopecoupled to a data source, such as for example an optical switch fabricsupplying data, for transport of the supplied data to a remote sitealong a direct line-of-site. At the remote site, a similar opticaltelescope can receive the incoming signal. Each telescope can operate ina bi-directional manner (e.g. for both sending an receiving of data). Inother examples, a transmitting telescope can be aimed at a secondidentical/reciprocal receiving telescope. The optical signal to betransmitted can emanate from a 1550 nm DFB type semiconductor laser andthen may be amplified with an optical amplifier typically through theuse of an erbium-doped fiber amplifier, (EDFA). For a more detaileddiscussion of conventional wireless optical systems see, for example, P.F. Szajowski, “Key Elements of High-Speed WDM Terrestrial Free-SpaceOptical Communications Systems,” SPIE Paper No. 3932-01, Photonics West(January 2000), which incorporated by reference herein.

As discussed above, current state-of-the-art free-space opticalcommunication systems are generally limited in reach and availabilitydue to optical power budgets as well as local atmospheric conditions,most notably fog related events. To address these and/or potentiallyother issues with currently available optical communication solutions,one or more implementations of the current subject matter providemethods, systems, articles or manufacture, and the like that can, amongother possible advantages, provide free-space optical communicationlinks while mitigating fog related and other similar effects that eventsthat can limit power detection limits. In some implementations, USPL1550 nm laser sources can be used within the framework of FSO transporthardware. An improved replacement optical transport technology canprovide enhanced optical budgets as well as link availability

Consistent with some implementation of the current subject matter, theoverall optical collection efficiency at a receiving site can beenhanced, thereby making the optical data-link more resistant toatmospheric effects, such as for example scintillation effects and fogattenuation effects. Furthermore, the USPL sources consistent withimplementations of the current subject matter are generally compatiblewith current telecommunications infrastructure components.

It can be an advantage of certain implementations of the current subjectmatter that previously encountered problems, for example insufficientpower and insufficient bandwidth due to fog and aerosol opticalimpairments with distance and atmospheric conditions, can be morereadily overcome. In overcoming these and other problems,implementations of the current subject matter can (among other possiblebenefits) provide techniques for multiplexing and de-multiplexing a FSObi-directional laser communication data link for single channel andwavelength division multiplexing (WDM) applications using USPL-FSO lasersources. Also included in the scope of the current subject matter is theuse of USPL-FSO laser sources as an out-of-band, or alternatively, anin-band tracking beacon.

USPL laser sources can be used, consistent with implementations of thecurrent subject matter, to address potential issues relating to systemavailability while propagating in the presence of fog or harmful aerosolenvironments. Using an USPL source, for example a 1550 nm USPL lasersource, in an FSO system can allow the USPL to be modulated in a similarmanner as conventional 1550 nm used throughout the telecommunicationindustry, for use in terrestrial, space, and undersea applications. USPLlaser sources used in conjunction with a FSO platform can provide anoptical wireless system with similar benefits in WDM configurations,thereby increasing the magnitude of effective optical bandwidth of thecarrier data link. Having the advantage of long-range opticalpropagation can require an equally robust optical tracking channel tomaintain optical co-alignment between optical terminals.

The output power of the transmitter can be increased by using singlemode optical amplifier type devices between the lasers and the focalplane of the transmitting telescope, regardless of whether the wirelessmedium is a multiple mode (multimode) medium. Such single mode opticalstructures can advantageously include one or more single mode opticalamplifiers to provide the necessary gain to the optical signal. Also, toprovide the needed increase in bandwidth, implementations of the currentsubject matter can send information over multiple modulated USPL lasersources at 1550 nm wavelengths, rather than the single wavelength ofcurrently available optical wireless techniques.

FSO transmit beams can be very narrow (3 milliradian and less), and anymotion between the terminals can cause misalignment and loss of signallink. FSO installations on mobile platforms (ground vehicle, air ship,marine ship, or satellite) therefore generally require a tracking systemto maintain alignment between the bi-directional FSO terminals. Towerinstallations and other non-stable stationary platforms can also requirea tracking system. Tracking systems can use a wide field-of-view CCD(charge coupled-device) or similar camera or other optical device, whichcan capture a transit beam pattern from another communication terminalin the x-y plane (the z-direction points directly to the other FSOterminal), and thereby calculate a centroid position of the beam on thecamera. If there is any relative motion between the FSO terminals, thecentroid position of the beam will shift from the center of the cameraplane. Either an external gimbal or internal steering mirrors can beadjusted accordingly to move the centroid back to the center of the CCDcamera plane, thereby keeping the FSO terminals aligned.

Legacy continuous wave (CW) FSO transmit beam patterns can be subject toatmospheric scintillation, which can cause the transmit beam to “dance”and “dart” around at distance. This effect can cause tracking systems tomove unnecessarily to compensate for the scintillation. In the worsecase, scintillation can cause beam power fade, which can disruptions tothe tracking system if it loses the beam all together. Experimentalobservations from USPL sources show a much more stable beam pattern withdistance. Using a USPL as a transmit source in a FSO system can lead toimprovement in tracking systems because of the much more stable beampattern. Excessive tracking motion can therefore be reducedsignificantly, thereby extending the lifetime of the mechanical trackingsystem. Scintillation fades can also be reduced or even eliminated usingan USPL in the FSO system, resulting in a more robust tracking systemwith reduced or eliminated signal loss and tracking disruption. Thetracking signal can either be modulated out-of-band (on a differentwavelength), or sent as a separate Ethernet signal and then incorporatedin the total Ethernet pipe between FSO terminals. Additionally, anout-of-band optical signal can be modulated with a data stream andmultiplexed to the overall capacity of the data link and can be used forthe purposes of tracking.

FIG. 1 illustrates an example of an optical communications platform 100consistent with an implementation of the current subject matter forusing an USPL device that is free-space coupled as an optical source fortransport. As shown in FIG. 1, a USPL source 102 is directly modulatedby an external source element 104. Optical power from the USPL source102 can be coupled across free space 110 to a transmitting element 106,optionally by an optical telescope. The transmitting element 106 canoptionally include optical components formed by hyperbolic mirrorfabrication techniques, conventional Newtonian designs, or the like. Areciprocal receiving telescope at a receiver system can provide foroptical reception. Consistent with implementations of the currentsubject matter, each optical transport platform can be designed tooperate as a bi-directional unit. In other words, the transmittingelement 106 of the optical communications platform 100 can also functionas a receiving element. In general, unless otherwise explicitly stated,a transmitting element 106 as described can be considered to also befunctional as a receiving element and vice versa. An optical elementthat performs both transmission and receiving functions can be referredto herein as an optical transceiver.

FIG. 2 illustrates an example of an optical communications system 200consistent with an implementation of the current subject matter thatincludes the optical communications platform 100 of FIG. 1. Also shownin FIG. 2 is a second complementary receiving element 204, which can bea receiving telescope located at a remote distance from the transmittingelement 106. As noted above, both the transmitting element 106 and thereceiving element 204 can be bi-directional, and each can function asboth a transmitting element 106 and a receiving element 204 depending onthe instantaneous direction of data transmission in the opticalcommunications system 200. This feature applies throughout thisdisclosure for transmitting and receiving elements unless otherwiseexplicitly stated. Either or both of the transmitting element 106 andthe receiving element 204 can be optical telescopes or other devices fortransmitting and receiving optical information.

FIG. 3 illustrates an example of an optical communications platform 300consistent with an implementation of the current subject matter forusing an USPL source 102 fiber coupled to an external modulator 302through a fiber medium 304 and connected to a transmitting element 106through an additional transmission medium 306, which can optionally be afiber medium, a free space connection, etc. The USPL source 102 can beexternally modulated by the external modulator 302 such that opticalpower from the USPL source 102 is fiber coupled to the transmittingelement 106 or handled via an equivalent optical telescope.

FIG. 4 illustrates an example of an optical communications system 400consistent with an implementation of the current subject matter thatincludes the optical communications platform 300 of FIG. 3. Also shownin FIG. 4 is a second complementary receiving telescope 204, which, asnoted above in relation to FIG. 2, can be a receiving telescope locatedat a remote distance from the transmitting element 106.

FIG. 5 illustrates an example of an optical communications architecture500 consistent with an implementation of the current subject matter. Thearchitecture 500 of FIG. 5 includes the elements of FIG. 4 and furtherincludes a first communication network 502 connected to a first opticalcommunications platform 300. The receiving element 204 is part of asecond optical communications platform 504, which can optionally includecomponents analogous to those of the first optical communicationsplatform 300. A second communications network 506 can be connected tothe second optical communications platform 504 such that the datatransmitted optically between the transmitting element 106 and thereceiving element 204 or are passed between the first and secondcommunications networks 502, 506, which can each include one or more ofoptical and electrical networking features.

FIG. 6 illustrates an example of an optical communications system 600consistent with an implementation of the current subject matter. As partof an optical communications platform 602, an USPL source 102 is fibercoupled to an external modulator 302, for example through an opticalfiber 202 or other transmission medium. The light from the USPL source102 is propagated via a transmitting element 106 in a similar manner asdiscussed above. An optical amplifier element 604, which can optionallybe an optical fiber amplifier element, can be used to increase opticaltransmit launch power, and can optionally be disposed between theexternal modulator 302 and the transmitting element 106 and connected toone or both via an additional transmission medium 306, which canoptionally be a fiber medium, a free space connection, etc. Also shownin FIG. 6 is a second complementary receiving element 206 located at aremote distance from the optical communications platform 602. It will bereadily understood that a second optical communications platform 504that includes the receiving element 204 can also include an opticalamplifier element 604. First and second communications networks 502, 506can be connected respectively to the two optical communicationsplatforms 602, 504

FIG. 7 illustrates an example of an optical communications system 700consistent with an implementation of the current subject matter. Theoptical communications platform 602 shown in FIG. 6 can be incommunication with a second optical communications platform 702, whichcan in this implementation include a receiving element 204 and anoptical preamplifier 704. Other components similar to those shown in theoptical communications platform 602 can also be included in the secondoptical communications platform 702, although they are not shown in FIG.7. It will be understood that a bi-directional optical communicationsplatform can include both of an optical preamplifier 704 for amplifyinga received optical signal and an optical amplifier element 604 forboosting a transmitted optical signal. Consistent with theimplementation depicted in FIG. 7 and other implementations of thecurrent subject matter, optical amplification (e.g. for either or bothof an optical amplifier element 604 or an optical preamplifier 704) beincluded for enhancing the optical budget for the data-link between thetransmitting element 106 and the receiving element 204 (and vice versa),for example using one or more of an erbium-doped fiber amplifier (EDFA),a high power erbium-ytterbium doped fiber amplifier (Er/Yb-DFA), orequivalents, which can include but are not limited tosemiconductor-optical-amplifiers (SOA).

FIG. 8 illustrates an example of an optical communications system 800consistent with an implementation of the current subject matter. Theoptical communications platform 602 shown in FIG. 6 can be incommunication with a second optical communications platform 802, whichcan in this implementation include a receiving element 204 and anoptical preamplifier 704 similar to those shown in FIG. 7. As shown inFIG. 8, the second optical communications platform 802 can furtherinclude optical receiver circuitry 804, which can receive amplified andelectrically recovered data received at the receiving element 204 andamplified by the optical preamplifier. A plurality of clock sources 806can interface to multiple remote multi-point network connections with aplurality of communications networks 810 as required. In a similarmanner, a complementary set of clock sources and multiple communicationnetworks can be operated in conjunction with the optical communicationsplatform 602 (e.g. in place of the single depicted communication network502 in FIG. 8.

FIG. 9 illustrates an example of an optical communications system 900consistent with an implementation of the current subject matter. Anoptical communications platform 902, which can feature similar elementsto those in the optical communications platform 602 first discussedherein in reference to FIG. 6, can also include an additional USPLsource 904 acting as a tracking and alignment (pointing) beacon source.A second optical communications platform 906 can also include anadditional USPL source 910 acting as a tracking and alignment (pointing)beacon source. The tracking and alignment (pointing) beacon sources 904,910 can optionally originate from available communications sources usedin data transport transmission, or can be provided by separate,dedicated USPL sources. In addition, each USPL beacon source 904, 910can include an in-band or out-of-band source, thereby allowing theadvantage of available optical amplification sources, or from dedicatedoptical amplification resources.

FIG. 10 illustrates an example of a FSO communication system 1000 thatincludes a dual polarization USPL-FSO optical data-link platform 1001 inwhich USPL sources are polarization multiplexed onto a transmittedoptical signal to thereby provide polarization multiplexed USP-FSO(PM-USP-FSO) functionality. Two USPL sources 102 and 1002 are fibercoupled to either directly modulated or externally modulated modulationcomponents 1004, 1006 respectively. Each respective modulated signal isoptically amplified by an optical amplifier component 1010, 1012followed by adjustment of optical polarization states using polarizationcomponents 1014, 1016. The polarization state signals are fiber coupledto a polarization dependent multiplexer (PDM) component 1020 forinterfacing to an optical launch platform component 1022, which can besimilar to the transmit element 106 discussed above. The PDM 1020multiplexes the light of differing polarization states into a singlepulse train for transmission via the optical launch platform component1022. An USPL optical beacon 904 can be included to provide capabilitiessimilar to those discussed above in reference to FIG. 9, for example tooperate along or in conjunction with a second USPL optical beacon 906 ata receiving platform 1024, which can include a receiving element 204similar to those described above. As previously noted, the receivingelement 204 as well as other features and components of the receivingplatform 1024 can generally be capable of supporting transmissionfunctions such that a bi-directional link is established. A receivedsignal recovered by the receiving element 204 can provide an opticalsignal that is interfaced to an appropriate polarization dependentde-multiplexer 1026 capable of providing two signals for further opticalamplification using amplification elements 1030, 1032. Each opticalamplified signal as provided by the amplification elements 1030, 1032can be interfaced to an appropriate optical network 1034, 1036 fornetwork usage.

FIG. 11A shows an example of a system 1100 in which USPL-FSOtransceivers can be utilized for use in line-of-sight opticalcommunication (e.g. “lasercom”) applications, and FIG. 11B shows anexample of a system 1150 in which USPL-FSO transceivers can be utilizedfor use in non-line-of-sight lasercom applications. An advantage to someimplementations of the current subject matter can be realized due toscattering of the optical signal sent from a transmit element as thetransmitted light passes through the atmosphere. This scattering canpermit the use of non-line-of-sight communication. In addition, radiosused in such communication systems can operate in the solar-blindportion of the UV-C band, where light emits at a wavelength of 200 to280 nm. In this band, when solar radiation propagates through theenvironment, it is strongly attenuated by the Earth's atmosphere. Thismeans that, as it gets closer to the ground, the amount of backgroundnoise radiation drops dramatically, and low-power communications linkoperation is possible. On the other hand, environmental elements such asoxygen, ozone and water can weaken or interrupt the communicationsbroadcast, limiting usage to short-range applications.

When UV waves spread throughout the atmosphere, they are typicallystrongly scattered into a variety of signal paths. Signal scattering isessential to UV systems operating in non-line-of-sight conditions, andthe communications performance can highly dependent on the transmissionbeam pointing and the receiver's field of view. A line-of-sightarrangement 1100 as shown in FIG. 11A can differ in bandwidth size froma non-line-of-sight arrangement 1150 as shown in FIG. 11B. Ultravioletcommunication can more strongly rely on a transmitter's beam positionand a receiver's field of view. As a result, refining of the pointingapex angle, for example by experimenting with supplementary equipment toenhance the UV-C signal, can be advantageous.

FIG. 12 illustrates an example of a remote sensing system 1200 in whichan USPL source 102 is fiber coupled by an optical fiber component 202 toan optical launch element 1202 capable of transmitting and receivingoptical signals. Some of the light propagated forward through theoptical launch element 1202 is backscattered by interaction withair-borne particulates that are the subject of investigation. Theoptical backscattered signal is detected through the optical launchelement 1202 or a similar receive aperture and passed along fordetection and spectrographic analysis through detection circuitry 1204or the like in FIG. 12. The signature of particulates within a targetatmospheric region 1206 within which an investigation is made can becalibrated through conventional approaches, for example usingpredetermined spectrographic calibration measurements based on one ormore of ultraviolet spectroscopy, infrared spectroscopy, Ramanspectroscopy, etc. Consistent with this implementation, an opticalsystem can be operated as a LiDAR instrument providing enhancedresolution and detection sensitivity performance, using USPL lasersources operating over a spectral range of interest. Adjustability ofspectral range can aid in evaluating and analyzing chemical constituentsin the atmosphere.

USPL-FSO transceivers can be utilized for remote sensing and detectionfor signatures of airborne elements using ionization or non-ionizationdetection techniques, utilizing optical transport terminals manufacturedthrough either the Hyperbolic Mirror Fabrication Techniques orconventional Newtonian designs that focus a received signal at one idealpoint. Also certain adaptations can be related to ionization probing ofremote regions include controllable ionization, which has been shown tooccur at these frequencies and an ionization process, which can befocused at distance to adjust depth of atmospheric penetrationespecially in weather and clouds.

FIG. 13 illustrates an example of use of USPL sources as well as opticalreception techniques to improve detection sensitivity. Researchers atthe National Institute of Standards and Technology (NIST), US, havebuilt a laser ranging system that can pinpoint multiple objects withnanometer precision over distances up to 100 km. The LIDAR (lightdetection and ranging) system could have applications from precisionmanufacturing on Earth to maintaining networks of satellites in perfectformation (Nature Photonics DOI: 10.1038/NPHOTON.2009.94). The NISTdevice uses two coherent broadband fiber-laser frequency combs.Frequency combs output a series of stable short pulses that also containa highly coherent carrier that extends across the pulse train. Thismeans a frequency comb can be employed to simultaneously make aninterferometric measurement as well as a time-of-flight measurement,thereby enhancing analytical capabilities for application specificsituations.

In the arrangement shown in FIG. 13, two phase-locked frequency combs1301 and 1302 are used in a coherent linear optical samplingconfiguration, also known as a multi-heterodyne, meaning that onefrequency comb measures both distance paths, while the other frequencycomb provides distance information encoded in the light of the firstcomb. Pulses from one frequency comb 1301 can be launched out of thefiber and directed towards two glass plates, a reference 1303 and atarget 1304. The plates 1303 and 1304 can reflect a certain fraction(e.g. approximately 4%) of the pulse back down the fiber, effectivelycreating two new pulses. The time separation between the two pulses 1301can give the distance between the moveable target plate and referenceplates. A second frequency comb 1302 is tightly phase-locked with thefirst, but has a slightly different repetition rate. Due to thedifferent delay between consecutive pulses when the sources interfere,the second frequency comb can sample a slightly different part of thelight from the electric field of the first comb.

Using the technique described is reference to FIG. 13, can make possiblethe replacement of two coherent broadband fiber-laser sources with twoappropriate USPL sources used within the scope of the configurationoutlined having each USPL source fiber coupled to dedicated free-spaceoptical telescope designs. By doing so, the overall efficiency, opticalranging and accuracy can be improved substantially.

Currently available USPL optical pulse trains operate at the nativepulse repetition rates of the USPL laser source and are typicallylimited to 50 MHz or less, thereby capping the maximum data rates foroptical transmission. As a result the optical system utilizing USPLlaser sources is restricted to low data rate applications of 50 Mbps orless. Having the means to increase USPL operational rates is necessaryfor providing solutions for data transport in excess of 50 Mbps.

FIG. 14 illustrates an example of a remote sensing system 1400 in whichan USPL source 102 is fiber coupled by an optical fiber component 202 toan optical launch element 1202 capable of transmitting and receivingoptical signals. Light propagated forward by the optical launch element1202 is backscattered by interaction with targets known and unknown thatare the subject of investigation within an atmospheric region 1206. Theoptical backscattered signal is detected through the optical launchelement 1202 or a similar receive aperture and passed along fordetection analysis through a detection circuitry and spectrographicanalysis component 1402 in FIG. 14. The signature of particulates withinthe region 1206 under investigation can be calibrated, for example whererange-finding analysis can be performed. A system 1400 as in FIG. 14 caninclude a USPL-FSO transceiver utilized and operated across the 1.3 to1.6 micron wavelength range as a range-finder and spotting apparatus forthe purposes of target identification and interrogation applications.

FIG. 15 illustrates an optical pulse multiplier module 1500 that canincrease the repetition rate of the output from a USPL source 102. Atypical USPL with a pulse width of 10-100 femto-seconds has a repetitionrate of, for example, 50 MHz. The output from the USPL 102 can be fed asan input 1502 into a USPL photonic chip pulse multiplier module 1504. Inthis example, the photonic chip can contain a 20,000:1 splitter element1506 that splits the input into discrete light elements. Each lightelement on the opposite side of the splitter element 1506 contains the50 MHz pulse train. Each light element then passes though a delaycontroller (either a fiber loop or lens array) 1510, which delays thepulse train for that element in time, for example by a number ofpicoseconds. Successive light elements are thereby delayed byincremental picoseconds. All of these pulse trains with their uniquetime delays are combined into a single pulse train in a fashion similarto time division multiplexing utilizing a 20,000:1 optical combinerelement 1512. The required ratios of splitters and combiners can becontrolled to provide necessary optical designs for the applicationrequired. The final output 1514 is a pulse train of 10-100 femto-secondpulses with a repletion rate of 1 THz. This THz pulse train can then bemodulated by a 10 or 100 GigE signal, such as shown in FIG. 28,resulting in 100 femto-second pulses per bit for the 10 GigE system, and10 femto-second pulses per bit for 100 GigE systems. The applicationcited is not limited to specific data rates of 10 and 100 Gbps, but canoperate as required by the application under considerations. Thesenumbers are just for illustration purposes. Implementations of thecurrent subject matter can use any multiplier factor to increase therepetition rate of the USPL via the photonic chip pulse multipliermodule 1504 to any arbitrary repetition rate. Other examples used ingeneration of enhanced USPL repetition rates are illustrated within thissubmission.

FIG. 16 depicts a system 1600 for generation, transmission, andreceiving of high pulse rate USPL optical streams. An optical chipmultiplexing module 1610, which can for example be similar to thatdiscussed in reference to FIG. 15, can be used in this application. Inthis approach to achieve USPL pulse multiplication, a series of 10 GigErouter connections (10 GigE is not intended to be a limiting feature)described by signals 1601, 1602, 1603, 1604 (four signals are shown inFIG. 16, but it will be understood that any number is within the scopeof the current subject matter) are interfaced to the optical chipmultiplexing module 1610. In operation, the optical chip multiplexingmodule 1610 can support full duplex (Tx and Rx) to connect with the 10GigE routers 1601, 1602, 1603, 1604. The optical chip multiplexingmodule 1610 can provide efficient modulation by a USPL signal 1685output from a USPL source 1690 for ingress optical signals 1601, 1602,1603, 1604. The optical chip multiplexing module 1610 can providecapabilities to modulate and multiplex these ingress optical signals.

At a remote receive site where a receiving device is positioned, allsignals sent via a transmitting element 1660 at the transmitting devicecan be recovered using an appropriate receiver element 1665. Acomplementary set of optical chip multiplexing module 1675 can providenecessary capabilities for demultiplexing the received data stream asshown by elements for delivery to a series of routers 1601′, 1602′,1603′, 1604′ (again, the depiction of four such routers is not intendedto be limiting). End-to-end network connectivity can be demonstratedthrough network end-point elements.

FIG. 17 depicts an example system 1700 in which an optical chip isinterconnected to a wavelength division multiplexing (WDM) system,currently available versions of which can be very expensive. WDM systemshave the advantage of not requiring timing or synchronization as neededwith a 10 GigE (or other speed) router 1701, since each 10 GigE signalruns independent of other such signals on its own wavelength. Timing orsynchronization of the TDM optical chip with 10 GigE routers can beimportant in a TDM optical chip. A GbE switch 1701 can provide thenecessary electrical RF signal 1705, from the switch 1701 to modulate aUSPL source 1702, either directly or by use of USPL a pulse multipliermodule previously detailed within this document. A typical NRZ output1710 can be coupled into a external modulator 1720, which can bemodulated using a NRZ clock source for the switch 1701, therebyresulting in a RZ modulated spectrum 1730. The conversion process usingreadily available equipment can provide capabilities for introducingUSPL sources and their benefits into the terrestrial backhaul networkspectrum.

For the optical chip system to successfully bridge between two remote 10GigE switches, it must typically act like a simple piece of fiber. Thetiming of the TDM chip can therefore be driven by the 10 GigE switch1701. Both actively mode-locked USPLs (i.e. 40 GHz, 1 picosecond pulsewidth) and passively mode-locked USPLs (i.e. 50 MHz, 100 USPL pulsewidth) can be driven by a RF timing signal.

FIG. 18 illustrates a device 1800 that can support another approach toprogression to a high pulse repetition data rate operation, such as forextremely high data rate operation in which optical chip design can beperformed using either fiber or free-space optics. A 50 MHz USPL source1801 is interfaced to a series of optical delay controller elements1802, which can be designed using either fiber loops or offset lenses,to result in producing exactly a 10.313 Gbps RZ output stream, which isthe 10 GigE line rate (greater than 10 Gbps because of 64 B/66 Bencoding). A splitter element 1803 provides splitting functionality ofthe incoming optical signal train 1801 into (in this example) 206 paths,along with variable optical delay lines 1804. After sufficient delay isintroduced through design all signals are multiplexed together through acombiner element 1805. In so doing a series of optical signals eachidentical, and equally spaced between adjacent pulses form a continuumof pulses for modulation. Prior to entering an E-O modulator element1806, all optical ingress signals can be conditioned by pre-emphasistechniques, for example using typical optical amplification techniques,to result in a uniform power spectrum for each egress signal from thecombiner element 1805. The conditioned egress signals are then coupledinto the E-O modulator element 1806 and modulated with an available NRZsignal from the 10 GigE signal source element 1807. The 10 GigEmodulated output 1809 can interface to an EDFA and then into the TX of aFSO system (or a fiber optic system). The Rx side (after the detector)can be fed directly into a 10 GigE switch as a modulated and amplifiedoutput 1810.

FIG. 19 illustrates another example of a device 1900 that can be usedfor USPL pulse multiplication consistent with implementations of thecurrent subject matter. Consistent with this approach, a 10×TDM systemis configured to give a 100 Gbps output. A TDM demux chip can be on thereceive side of a communication link to break up the individual 10 GigEsignals, and can include a reciprocal approach to the design shown inFIG. 19.

As in FIG. 18, a 50 MHz USPL source 1801 is interfaced to a series ofoptical delay controller elements 1802, which can be designed usingeither fiber loops or offset lenses, to result in producing exactly a10.313 Gbps RZ output stream, which is the 10 GigE line rate (greaterthan 10 Gbps because of 64 B/66 B encoding). A splitter element 1803provides splitting functionality of the incoming optical signal train1801 into (in this example) 206 paths, along with variable optical delaylines 1804. After sufficient delay is introduced through design allsignals are multiplexed together through a combiner element 1805.Instead of a single modulator element 1806 as shown in FIG. 18, however,the 10.313 GHz RZ output 1901 from the combiner element 1805 is fed intoa second splitter element 1910, which in this case can be a 10×splitter, which splits the optical signal into ten parallel paths. Otherimplementations of this design can support various split ratios asrequired by design. Optical paths out from second splitter element 1910are individually connected to specified optical delay lines 1920. Eachindividual delayed path is connected to a dedicated optical modulator ofa set of optical modulators 1930 modulated with an available NRZ signalfrom the 10×10 GigE signal source element 1931, resulting in a series ofmodulated optical signals 1935. An optical combiner identified 1940provides a single optical pulse train 1950. The series of optical pulsesin the single optical pulse train 1950 can be interfaced to anappropriate optical amplifier for desired optical conditioning fornetwork use.

FIG. 20 illustrates another example of a device 2000 that can be usedfor USPL pulse multiplication consistent with implementations of thecurrent subject matter. A device 2000 as depicted can provide theability to achieve high USPL pulse repetition data rates for networkapplications by modulation of the low repetition rate intra-channelpulses. By applying direct modulation of each channel on the delaycontroller, creation of a modulation scheme, which is not constrained bythe current speed limitations from the electronics technology, can bebeneficially accomplished. Implementations of the current subject mattercan provide a mechanism to enhance the data transmission capacity of asystem, by separately modulating individual channels at the currentstandard electronic modulation speed (in the example of FIG. 20 at therate of 100×10 GigE signal input 2001) and time-multiplexing thechannels into a single frequency high rep rate pulse stream. In thisapproach, the current standard, which is limited by the speed ofelectro-optic modulators (40 Gbps), can be enhanced by approximately Norders of magnitude, where N is the number of channels of thetime-multiplexer. For example, a 100 channel TDM with each channelamplitude modulated at the current standard data rate can be able tooffer data rates at speeds of up to 4 Tbs. N can be limited by the widthof the optical pulse itself. In the limit that information is carried 1bit/pulse, the time slot occupied by 1 bit is the width of the pulseitself (in that sense, RZ system would converge to a NRZ). For example,in the scheme, a 40 fs pulse width laser with a 40 GHz rep rate is ableto carry information at a maximum rate of 25 Tbps. This approach can beused in a 40 Gbps-channel modulation scheme (i.e 1 bit every 25 ps) andcan correspond to a capacity of N˜625 channels in a single transmission,which can be the number of 40 fs time intervals fitting in a 25 ps timeinterval. A significant advantage of this approach is the ability to“optically enhance” an otherwise limited data capacity modulationscheme, while still interfacing with the existing data rate limitedmodulators. For example, an amplitude modulator based on a Mach-Zehnderinterferometer can be easily integrated in a TDM IC package, in thatrequired is the ability to branch out the channel into two separatepaths, add a tiny phase modulator (nonlinear crystal) in one of thepaths, and combine the paths for interference.

FIG. 20 includes a USPL source 2010 coupled to a multi-port opticalsplitter element 2020. The number of optical ports identified need notbe limited to those described or shown herein. A series of optical delaylines 2030 provide required optical delays between each parallel pathfrom the multi-port optical splitter element 2020, and can be tailoredfor specific applications. The optical delay paths from the opticaldelay lines 2030 are summed together using an optical combiner element2035. The resulting combined optical data stream appearing throughelement 2040 represents a multiplicative enhancement in the pulserepetition rate of the original USPL source identified by element 2010.Further enhancement in pulse repetition rate is accomplished though theusage of element 2041, described by an optical splitter where theincoming signal 2040 is split into a series of paths not limited tothose identified by element 2041. By way of a second delay controller2045, optical delays may be introduced to each path within the device asidentified by the second set of optical delay paths 2042. Each parallelpath 2042 in turn is modulated by a modulating element 2044 with anavailable RF signal source element identified by the signal input 2001.An optical combiner element 2050 integrates all incoming signals onto asingle data stream 2060.

Optical pre-emphasis and de-emphasis techniques can be introduced withineach segment of elements described to custom tailor the optical spectrumfor a uniform or asymmetric optical power distribution. Pre- &de-emphasis can be accomplished using commonly used optical amplifierssuch as Er-Doped Optical amplifiers (EDFA).

FIG. 21 depicts an example of a system 2100 that includes a mode-lockedUSPL source 2101, which can be used to generate appropriately requiredclock and data streams for the application. Mode-locked lasers canrepresent a choice of high performance, high finesse source for clocksin digital communication systems. In this respect, mode-locked fiberlasers—in either linear or ring configuration—can make an attractivecandidate of choice, as they can achieve pulse widths on the USPL sourceregion and repetition rate as high as GHz. In addition to that, fibersoffer compactness, low cost, low sensitivity to thermal noise, lowjitter, no problems associated with diffraction or air dust pollution,just to name a few. In a communications scenario, the pulse width candetermine the available bandwidth of the system, and the repetition ratelimits the data rate. The pulse width can be determined by the intrinsiccharacteristics of the laser cavity—i.e. balancing of the overallgroup-velocity dispersion (GVD), and the choice of the saturableabsorber (in the case of a passive system)—or the bandwidth of an activeelement (in the case of an active mode-locked system). The repetitionrate of the pulse train is constrained by the length of the fiber. Forexample, in a linear laser, the fundamental mode v_(osc) of the lasercan be expressed as:

$\begin{matrix}{{v_{OSC} = \frac{c}{2\; n_{g}L}},} & (4)\end{matrix}$

where c is the speed of light in vacuum, n_(g) is the average groupindex, and L is the length of the cavity. Therefore, a 10 cm long fiberlaser cavity element 2110 with an average group index of 1.47 would havea repetition rate of 1 GHz. In strictly passive systems, mode-lockingcan be achieved through the use of a saturable absorber. In an activelaser, an amplitude modulator element 2150 can be inserted in the cavityto increase the repetition rate of the laser (harmonic mode locking). Inorder to achieve high repetition rate clocks using mode-locked USPLsource, it is possible to use one or more of (i) an intra-cavityamplitude Mach-Zehnder modulator (MZM) 2150 as shown in FIG. 21 and (ii)a low threshold saturable absorber. These techniques, known as “harmonicmode-locking”, can be utilized within a fiber based plant distributionsystem or within a FSO system, for terrestrial, submarine or FSO systemeither in; air, space or submarine applications.

Detailed within FIG. 21 is 980 nm pump element 2102 coupled to anoptical WDM device 2105. An erbium doped optical amplifier 2110 orequivalent can be used to create a non-linear environment to obtain amode-locked pulse train emission within a closed cavity establishedbetween two Faraday reflectors 2101 and 2160 on either end of theoptical USPL cavity. Operation of the device is capable of establishinga self-contained series of optical pulse in excess of 100 Gbps, andhighly synchronized in nature at the output port 2170 of the module. Inorder to achieve a high gain non-linear medium the EDFA 2110 can bespecially designed. A phase lock loop 2130 can provide advantageousstability in operation by maintaining a synchronized clock sourcethrough modulation of the signal through components 2120, 2130, 2150 ofthe self contained high-repetition rate pulse generator.

To achieve high rep rates in a laser that is limited by its dimensions(length in the case of a linear laser and perimeter in the case of aring laser), it can be necessary to stimulate intra-cavity generation ofthe multiples of the fundamental mode. In the active case, an amplitudemodulator inserted in the cavity modulates the loss of the systemoperating as a “threshold gating” device. For this approach to besuccessful, it can be necessary that the controlling signal to themodulator be referenced to the oscillation of the laser itself to avoidthe driving signal “forcing” an external frequency of oscillation on thelaser. This can be realized by the introduction of a phase-lock-loopelement 2130, or a synchronous oscillator circuit to track-and-lock ontothe repetition rate of the laser, and regenerate the signal. In the caseof a PLL, the RF output can be set to a multiple of the input signal(much as this device is used in cell phone technology), and the rep rateof the laser increased. The signal can then be used for triggering of apulse generator, or in conjunction with a low-pass filter. A MZamplitude modulator 2150 outside the laser cavity can be used to createOn-Off Keying (OOK) modulation on the pulse train coming out of themode-locked laser.

FIG. 22 shows a graphical depiction 2200 illustrating effects of a lossmodulation introduced to the input pulse train 2201 due to the presenceof the amplitude modulator 2205 with a controlling signal NRZ signal2210 made of a bit sequence as illustrated. The resulting signal at theoutput of the device 2220 represents an NRZ to RZ converter device foruse in telecommunications and scientific applications where theapplication may benefit from RZ data streams. A clock signal 2201(optical input) at a given pulse repetition rate will pass through themodulator 2205. At the same time, a controlling signal consisting of asequence of 1's and 0's can be applied to the RF port of the modulatorelement 2215. When the modulator element 2215 is biased at minimumtransmission, in the absence of a controlling signal the lossexperienced by the optical signal can be at its maximum. In the presenceof the RF signal (1's), the loss will drop to a minimum (OPEN GATE),thus working as an On-Off Keying modulation device. The pulse width ofthe output optical signal is typically much less than the time slotoccupied by a single bit of information (even less than a half clockperiod of a NRZ scheme) making this system genuinely RZ as identified byelement 2220.

FIG. 23 illustrates an example system 2300 for generation of highoptical harmonic USPL pulse streams having high pulse repetition rateusing a saturable absorber (SA) device 2330. The SA device 2330 can insome examples include carbon nano-tubes. Passive mode-locked fiberlasers using carbon nano-tubes SA (CNT-SA) make another attractiveoption for high rep rate sources due to their ability to generate highharmonics of the fundamental rep rate. In the approach described, aclosed, self contained optical cavity is established, in which twoFaraday reflectors 2301 and 2350 form the optical cavity. Although ahigh-power erbium doped fiber amplifier (EDFA) 2310 is shown in FIG. 23,any inverting medium producing a non-linear optical cavity can be used.A seed laser 2315, such as for example a 980 nm pump laser as shown inFIG. 23 can be used in generating a high-repetition rate optical train.In particular, any suitable pump laser may be considered in terms ofoptical wavelength and pulse repetition rate required. The SA element2330 can be placed within the cavity to establish required optical pulsecharacteristics 2350 as required through design requirements.

FIG. 23 shows the schematics of an example of a laser that can be usedin one or more implementations of the current subject matter. Unlike theactive laser shown in FIG. 22, here the MZ modulator can be replaced bythe SA element 2330. A technique similar to those described herein canbe utilized within a fiber based plant distribution system or within aFSO system, for terrestrial, submarine or FSO system either in air,space or submarine applications.

FIG. 24 illustrates an approach to providing time-domain multiplexing(TDM) where the TDM multiplexes a pulse train using parallel time delaychannels. In some instances, it can become important to manipulate thedelay channels such that they are “consistent” relative to each another.The frequency of the output multiplexed pulse train can ideally as muchas possible be insensitive to environmental changes. For that, aproposed feedback loop control system is design to correct the delayunits for any fluctuations which compromises the stability of the outputrep rate.

FIG. 24 shows a diagram of an example of a delay control system 2400.The control loop can be implemented in one of several ways consistentwith the current subject matter. FIG. 24 describes one possibility forillustration purposes. The input pulse train enters the TDM andmultiplexes into N paths, each with its own delay line. If the paths aremade of low “bending-loss” fiber waveguides, then each path can becoiled around a cylindrical piezoelectric actuator (PZ) of radius R. Theactuators generally expand in a radial direction as a result of acontrolling voltage (Vc). This expansion ΔR, which is linearlyproportional to Vc, causes a change in length of the fiber ΔL=2πNΔR,where N is the number of fiber turns around the PZ. For Terahertzmultiplexing, the delay between the pulses (and thus of PZ1) must be 1picosecond. This can require a change in length equals to 200 microns,which, for a one turn PZ actuator corresponds to a ΔR=32.5 microns. Mostcommercially available piezoelectric actuators are highly linear andoperate well within this range. The control mechanism can, therefore, bebased on several PZ actuators, each with a number of turns correspondingto multiples of the first delay, i.e. (32, 64, 96 microns, etc.), andcontrolled by a single voltage Vc. The controlling voltage is determinedby the feedback system, which compares the frequency of the outputsignal using a 1/N divider, with the frequency of the input signal,using a phase comparator (PC). The frequency of the “slow” input opticalsignal (represented by the waveform with τRT in FIG. 24 is converted toan RF signal using photo-detector PDin. In order to reduce the effectsof electronic jitter, a “differentiator” (or high pass filter) can beapplied to the RF signal as to steepen the leading edges of the pulses.A phase-locked loop is used to track-and-lock the signal, and toregenerate it into a 50% duty-cycle waveform. Likewise, in the outputside, the optical signal is picked-up by photo-detector PDout, high-passfiltered, and regenerated using the clock output port of aclock-and-data recovery system. The clock of the output signal, whichhas a frequency N times the frequency of the input signal, is send to anN times frequency divider before going to the phase comparator. From thephase comparator, a DC voltage level representing the mismatch betweenthe input and output signals (much as what is used in the architectureof PLL circuits) indicates the direction of correction for theactuators. A low-pass filter adds a time constant to the system toenhance its insensitivity to spurious noise.

A CDR can advantageously be used in the output, as opposed to a PLL suchthat the output signal may, or may not, be modulated. This system can bedesigned to work in both un-modulated, and “intra-TDM modulated” (i.e.one modulator at each delay path) schemes. However, this is a completelydeterministic approach to compensating for variations on the length ofthe delay lines. Ideally, and within a practical standpoint, the delaypaths should all be referenced to the same “thermal level” i.e. besensitive to the same thermal changes simultaneously. In the event thateach line senses different variation, this system would not be able tocorrect for that in real time.

In the alternative, a completely statistical approach can includesumming of op amp circuits (S1 . . . SN) to deliver the controllingvoltage to the actuators. Using such an approach, input voltages (V1 toVN) can be used to compensate for discrepancies in length between thelines, in a completely static sense, otherwise they can be used forinitial fine adjustments to the system. The approach typically must alsocompensate or at least take into account any bending loss requirementsof the fibers used. Some new fibers just coming out in the market mayhave a critical radius of only a few millimeters.

In the event that each path delay line senses different variation intemperature or experiences uncorrelated length changes due to spuriouslocalized noise, the previously described approach, as is, may sufferfrom difficulties in performing a real time correction. A more robustapproach operating in a completely statistical sense can be usedconsistent with some implementations of the current subject matter. Insuch an approach, summing op amp circuits (S1 . . . SN) can be used todeliver the controlling voltages to the actuators. In this case, theinput voltages (V1 to VN) can be used to compensate for discrepancies inlength between the delay lines in a completely statistical sense,otherwise they can only be useful for initial fine adjustments to thesystem (calibration).

Referring again to FIG. 24, an incoming USPL source identified aselement 2401 is coupled to an optical coupler element 2403, such thatone leg of the coupler connects to an optical photodiode selected foroperation at the operational data rate of 2401. Using standardelectronic filtering techniques described by elements 2404, 2405, and2406 an electrical square wave representation of the incoming USPLsignal is extracted and identified by element 2407. The second opticalleg of coupler 2403 is interfaced into an appropriate optical splitterelement identified by 2410, where the incoming signal into 2410 is splitinto 206 parallel optical paths. Also illustrated are variable rateoptical delay lines established in parallel for each of the parallelbranches of the splitter element 2410. The parallel piezo-electricelectric elements are identified by elements 242N and are controlledelectronically through feedback circuitry within the diagram. A controlvoltage identified by Vc is generated through a photodiode 2485 alongwith electronic circuitry elements 2480 and 2475. The clock-and-dataRecovery (CDR) element 2475 produces a clock source that is used incontrolling each of the PZ elements. Optical paths identified as 244Nare combined after a proper delay is introduced into each leg of element2410. The pulse multiplied USPL signal 2490 is thereby generated.

FIG. 25A shows a schematic of a fiber PZ actuator 2500, and FIG. 25Bshows a graph 2590 of radius vs. voltage for such an actuator. Together,these drawings illustrate operation of a PZ actuator for increasing thepulse repetition rate of an incoming USPL pulse train through inducedoptical delay. Although shown for use as an element for enhancing pulserepetition rate generation for USPL signals, the same technique can beused for other optical devices requiring or benefiting from opticaldelay. The basic structure for the device is a fiber based PZ actuator2501. When a voltage 2550 is applied to electrodes 2520 a voltageinduced stress results within the fiber, causing a time delay of theoptical signal traveling through the fiber. By varying applied voltage aperformance curve of optical delay vs. applied voltage is obtained asshown in the graph 2590 of FIG. 25B.

FIG. 26 shows a diagram illustrating features of an example statisticalcorrector 2600. The coarse correction controller 2640 shown in FIG. 26corresponds to the system described in the previous section, which cancorrect for length variations simultaneously picked up by all delaylines. As mentioned, these variations are expected to occur in a timescale much slower than the “intra delay line” spurious variations. Thislatter effect can manifest itself as a period-to-period jitterintroduced on the system. This type of jitter can be monitored using anRF Spectrum Analyzer (RFA), causing the rep rate line of the system todisplay “side lines” (or side bands), which are the result of theanalyzer beating together noisy frequencies resulting from uneven timeintervals between consecutive pulses. One such pattern can be processedusing an analog-to-digital converter (ADC) and saved as an array ofvalues, which can then be fed to a neural network (NN) machine. Neuralnetwork machines are known to posses excellent adaptabilitycharacteristics that allow them to essentially learn patterns fromoutside events by adapting to new set of input and outputs. A set ofinputs in this case can be generated from a set of “imperfectobservations”, i.e. “noisy” outputs of the TDM system as detected by theRFA and converted to digital arrays by the ADC ({f₁,f₂, . . . f_(N)},where f_(i) is a frequency component picked up by the RFA). A set ofoutputs can be generated from the corrections ({V₁, V₂, . . . , V_(N)},where V_(i) is a compensating input voltage to the summing op amp)required to rid the output frequency set from the undesired excessfrequency noise, which is due to the outside perturbations to thesystem. With a sufficiently large number of {f,V} pairs, where f, V arefrequency, voltage arrays, one can build an statistical set to train theNN machine to learn the underlying pattern associated with the presenceof the intra-channel noise. These machines can be found commercially inan IC format from several manufacturers, or implemented as software andused in conjunction with a computer feedback control mechanism. A singlelayer Perceptron type neural network, or ADALINE (Adaptive Linear Neuronor later Adaptive Linear Element), should be sufficient to accomplishthe task.

Similar to the description provided above in relation to FIG. 24, astatistical corrector element 2670 can include electronic circuitry thatis similar to or that provides similar functionality as the electricalcircuitry elements 2480 and 2475 and the photodiode 2485 of FIG. 24. Forthe approach illustrated in FIG. 26, a RF spectra analyzer 2695 alongwith a Neural Network 2670 and a Coarse Correction Controller element2640 are used to perform the requirement of optical delay introducedinto a parallel series of PZ elements 262N.

FIG. 27 illustrates concepts and capabilities of approaches consistentwith implementations of the current subject matter in which performance,accuracy, and resolution can be improved through replacement ofpiezoelectric disk (PZ) modules identified by elements 2795 and 272N,where compact micro fiber based collimators (MFC) 2795 encircled byceramic disks are used to obtain optical delay lines. Althoughillustrating a technique for increasing the native pulse repetition ratefor a USPL pulse train, the design illustrated is not limited to suchapplications but can be applied or extended to other needs within theoptical sector wherever optical delay is required. In so doing, a morecontrolled amount of temporal delay can be introduced within each MFCelement of the circuit. The improvement through the use of utilizing MFCelements can improve response, resolution, and the achievement ofreproducing in a rapid fashion required voltage responses in a massproduction means. The concept identified within FIG. 27 can beincorporated into precisely produced elements that can serve ascomplementary paired units for use in reducing USPL pulse-to-pulsejitter as well as for the purposes of data encryption needs.

With further reference to FIG. 27, a USPL source 2701 having a certainpulse repetition rate is split into a preselected number of opticalpaths 271N (which can number other than 206) as identified by splitterelement 2705. An appropriately controlled delay 273N is introduced intoeach parallel leg of the split optical paths 271N using elementsdescribed by 2795 and 272N. The resulting delayed paths 274N are addedtogether through an optical combiner element 2760. The pulse multipliedUSPL signal 2780 results.

One potential disadvantage of some previously available TDM designs, inwhich fibers are “wrapped-around” the piezo actuators, is that themechanism must comply with the bending loss requirements of the fibersused. Some new fibers just coming out in the market have critical radiusof only a few millimeters. To correct for this issue, implementations ofthe current subject matter can use of micro-machined air-gap U-bracketsin lieu of the fiber-wrapped cylindrical piezos. FIG. 27 illustratesthis principle. In this approach, the piezoelectric actuators (PZ_(I), .. . PZ_(N)) can be replaced by air gap U-bracket structures constructedusing micro-fiber collimators (MFCs), and micro-rings made of apiezoelectric material. In this case, however, the piezoelectricactuator expands longitudinally, increasing (or decreasing) the air gapdistance between the collimators, in response to the controllingvoltages (V1, V2, . . . VN). As in the case of the cylindricalpiezoelectric, a single voltage Vc can be use to drive all thepiezoelectric devices, provided that the gains of each channel (G1, G2,. . . GN) are adjusted accordingly to provide the correct expansion foreach line. Ideally, except for inherent biases to the system (i.e.intrinsic differences between op amps), the gain adjustments should beas G1, 2G1, 3G1, and so forth, in order to provide expansions, which aremultiples of the τRT/N. Another way of implementing such an approach canbe the use of multiple piezoelectric rings at the channels. In thatmanner, one can have channels with 1, 2, 3, N piezoelectric rings drivenby the same voltage with all amplifiers at the same gain.

FIG. 28 provides a conceptual presentation of an optical chip system2800 to successfully bridge between two remote 10 GigE switches.Ideally, such a connection can perform similarly to a simple piece offiber. The timing of the TDM chip can be driven by the 10 GigE switch.

In reference to FIG. 28, a USPL source 2805 having a predeterminednative pulse repetition rate identified by 2806 connects to an opticalPulse multiplier chip 2807. Element 2807 is designed to convert theincoming pulse repetition rate signal 2806 into an appropriate level foroperation with high-speed network Ethernet switches as identified by2801. Switch 2801 provides a reference signal 2802 used to modulatesignal 2809 by way of a standard electro-optic modulator 2820 at thedata rate of interest. A resulting RZ optical signal is generated asshown in element 2840.

An alternative to having the timing run from the 10 GigE switch is tobuild up the USPL to a Terabit/second (or faster) with a multiplierphotonic chip, and then modulate this Terabit/second signal directlyfrom the 10 GigE switch. Each bit will have 100 or so pulses. Anadvantage of this approach can be the elimination of a need for separatetiming signals to be run from the switch to the USPL. The USPL viamultiplier chip just has to pump out the Terabit/second pulses. Anotheradvantage is that the output of the Multiplier Chip does not have to beexactly 10.313 or 103.12 Gbps. It just has to at a rate at about 1Terabit/second. Where each 10 GigE bit has 100 or 101 or 99 pulses, thislimitation is a non-issue. Another advantage is each bit will have many10 USPL, so the 10 GigE signal will have the atmospheric propagation(fog and scintillation) advantage. Another advantage can be realized atthe receiver end. It should be easier for a detector to detect a bit ifthat bit has 100 or so USPL pulses within that single bit. This couldresult in improved receiver sensitivity, and thus allow improved rangefor the FSO system. An additional advantage can be realized in thatupgrading to 100 GigE can be as simple as replacing the 10 GigE switchwith a 100 GigE switch. Each bit will have around 10 pulses in thiscase.

From a purely signal processing perspective this approach demonstratesan efficient way to send data and clock combined in a singletransmission stream. Much like a “sampling” of the bits using an opticalpulse stream, this approach has the advantage that the bit “size” isdetermined by the maximum number of pulses the it carries, thereforeestablishing a basis for counting bits as they arrive at the receivingend. In other words, if the bit unit has a time slot which can fit Npulses, the clock of the system can be established as “one new bit ofinformation” after every 5^(th).

A technique similar to those described herein can be utilized within afiber based plant distribution system or within a FSO system, forterrestrial, submarine or FSO system either in air, space or submarineapplications, and illustrates for the first time how the interconnectionfrom USPL sources to optical network elements is achieved for networkingapplications.

FIG. 29 shows a system 2900 that illustrates a conceptual networkextension for the design concept reflected within FIG. 28. As multipleUSPL sources 2901, 2902, 2903 (it should be noted that while three areshown, any number is within the scope of the current subject matter),each modulated through dedicated optical switches and USPL laserMultiplier Chips circuits are configured in a WDM arrangement. Asdescribed in reference to FIG. 28, electrical signals from each Ethernetswitch can be used to modulate dedicated optical modulators 2911, 2922,2928 for each optical path. Optical power for each segment of the systemcan be provided by optical amplification elements 2931, 2932, 2933 foramplification purposes. Each amplified USPL path can then be interfacedto an appropriate optical combiner 2940 for transport to a network 2950,and can be either free space or fiber based as required. The output fromthe WDM module can then be configured to a transmitting element 102 forFSO transport or into fiber plant equipment.

The technique described herein can be utilized within a fiber basedplant distribution system or within a FSO system, for terrestrial,submarine or FSO system either in; air, space or submarine applications,and illustrates for the first time how the interconnection from USPLsources to optical network elements is achieved for networkingapplications.

FIG. 30 shows the schematics of an experimental setup forimplementations of the current subject matter to include construction ofa computer assisted system to control the pulse width of an all-fibermode-locked laser using recursive linear polarization adjustments withsimultaneous stabilization of the cavity's repetition rate using asynchronous self-regenerative mechanism. The design can also offertune-ability of the repetition rate, and pulse width.

The fiber ring laser is represented by the inner blue loop, where allintra-cavity fiber branches are coded in blue, except for the positivehigh dispersion fiber outside the loop, which is part of the fibergrating compressor (coded in dark brown). The outside loops representthe feedback active systems.

FIG. 30 shows a diagram of a system 3000 illustrating features of anUSPL module providing control of pulse width and pulse repetition ratecontrol through mirrors (M1, M2), gratings (G1,G2), lengths (L1,L2),second-harmonic generator (SHG), photomultiplier tube (PMT), lock-inamplifier (LIA), data acquisition system (DAC), detector (DET),clock-extraction mechanism (CLK), frequency-to-voltage controller (FVC),high-voltage driver (HVD), reference signal (REF), pulse-generator(PGEN), amplitude modulator (AM), isolator (ISO), piezoelectric actuator(PZT), optical coupler (OC), polarizer (POL), and polarizationcontroller (PC) all serve to provide control of pulse repetition rateand pulse width control.

The passive mode-locking mechanism can be based on nonlinearpolarization rotation (NPR), which can be used in mode-locked fiberlasers. In this mechanism, weakly birefringent single mode fibers (SMF)can be used to create elliptically polarized light in a propagatingpulse. As the pulse travels along the fiber, it experiences a nonlineareffect, where an intensity dependent polarization rotation occurs. Bythe time the pulse reaches the polarization controller (PC) 3001 thepolarization state of the high intensity portion of the pulseexperiences more rotation than the lower intensity one. The controllercan perform the function of rotating the high intensity polarizationcomponent of the pulse, bringing its orientation as nearly aligned tothe axis of the polarizer (POL) as possible. Consequently, as the pulsepasses through the polarizer, its lower intensity components experiencemore attenuation than the high intensity components. The pulse comingout of the polarizer is, therefore, narrowed, and the entire processworks as a Fast-Saturable Absorber (FSA). This nonlinear effect works inconjunction with the Group-Velocity Dispersion (GVD) of the loop, and,after a number of round trips, a situation of stability occurs, andpassive mode-locking is achieved. The overall GVD of the optical loopcan be tailored to produce, within a margin of error, an specificdesired pulse width, by using different types of fibers (such as singlemode, dispersion shifted, polarization maintaining, etc. . . . ), andadding up their contributions to the average GVD of the laser.

An active control of the linear polarization rotation from the PC cangreatly improve the performance of the laser. This can be achieved usinga feedback system that tracks down the evolution of the pulse width.This system, represented by the outer loop in FIG. 1, can be used tomaximize compression, and consequently, the average power of the pulse.A pulse coming out of the fiber ring laser through an OC is expected tohave a width on the order of a few picoseconds. An external pulsecompression scheme, which uses a fiber grating compressor, is used tonarrow the pulse to a sub 100 fsec range. This technique has beenextensively used in many reported experiments, leading to high energy,high power, USPL pulses. Here, the narrowed pulse is focused on aSecond-Harmonic Generator (SHG) crystal and detected using aPhoto-Multiplying Tube (PMT). The lock-in-amplifier (LIA) provides anoutput DC signal to a Data Acquisition Card (DAC). This signal followsvariations of the pulse width by tracking increases, or decreases, inthe pulses' peak power. A similar technique has been successfully usedin the past, except that, in that case, a Spatial Light Modulator (SLM)was used instead. Here, a programmable servo-mechanism directly controlsthe linear polarization rotation using actuators on the PC. With the DCsignal data provided by the DAC, a decision-making software (such as,but not limited to, LABVIEW or MATLAB SIMULINK) can be developed tocontrol the servo-mechanism, which in turn adjusts the angle of rotationof the input pulse relative to the polarizer's axis. These adjustments,performed by the actuators, are achieved using stress inducedbirefringence. For instance, if the pulse width decreases, the mechanismwill prompt the actuator to follow a certain direction of the linearangular rotation to compensate for that, and if the pulse widthincreases, it will act in the opposite direction, both aimed atmaximizing the average output power.

A self-regenerative feedback system synchronized to the repetition rateof the optical oscillation, and used as a driving signal to an amplitudemodulator (AM), can regulate the round trip time of the laser. In theactive system, the amplitude modulator acts as a threshold gating deviceby modulating the loss, synchronously with the round trip time. Thistechnique has can successfully stabilize mode-locked lasers in recentreports. A signal picked up from an optical coupler (OC) by aphoto-detector (DET) can be electronically locked and regenerated by aclock extraction mechanism (CLK) such as a Phase-Locked Loop or aSynchronous Oscillator. The regenerated signal triggers a PulseGenerator (PGen), which is then used to drive the modulator. In aperfectly synchronized scenario, the AM will “open” every time the pulsepasses through it, at each round trip time (TRT). Because the CLKfollows variations on TRT, the driving signal of the AM will varyaccordingly.

An outside reference signal (REF) can be used to tune the repetitionrate of the cavity. It can be compared to the recovered signal from theCLK using a mixer, and the output used to drive a Piezoelectric (PZT)system, which can regulate the length of the cavity. Such use of a PZTsystem to regulate the cavity's length is a well known concept, andsimilar designs have already been successfully demonstratedexperimentally. Here a linear Frequency-to-Voltage Converter (FVC) maybe calibrated to provide an input signal to the PZT's High VoltageDriver (HVD). The PZT will adjust the length of the cavity to match therepetition rate of the REF signal. If, for instance the REF signalincreases its frequency, the output of the FVC will decrease, and sowill the HV drive level to the piezoelectric-cylinder, forcing it tocontract and, consequently increasing the repetition rate of the laser.The opposite occurs when the rep. rate of the reference decreases.

It is possible to have the width of the pulse tuned to a“transformed-limited” value using a pair of negative dispersiongratings. This chirped pulse compression technique is well established,and there has been reports of pulse compressions as narrow as 6 fs. Theidea is to have the grating pair pulse compressor mounted on a movingstage that translates along a line which sets the separation between thegratings. As the distance changes, so does the compression factor.

In an example of a data modulation scheme consistent withimplementations of the current subject matter, a passively modelockedlaser can be used as the source of ultrafast pulses, which limits ourflexibility to change the data modulation rate. In order to scale up thedata rate of our system, we need to increase the base repetition rate ofour pulse source. Traditionally, the repetition rate of a passivelymodelocked laser has been increased by either shortening the lasercavity length or by harmonic mode-locking of the laser. Both techniquescause the intra-cavity pulse peak power to decrease, resulting in longerpulse-widths and more unstable mode-locking.

One approach to solving this problem involves use of a modified pulseinterleaving scheme, by a technique which we call pulse multiplication.FIG. 31 illustrates this concept. The lower repetition rate pulse trainof a well-characterized, well-modelocked laser 3101 is coupled into anintegrated-optical directional coupler 3180, where a well-determinedfraction of the pulse is tapped off and “re-circulated” in an opticalloop with an optical delay 3150 equal to the desired inter-pulse spacingin the output pulse train, and re-coupled to the output of thedirectional coupler. For instance, to generate a 1 GHz pulse train froma 10 MHz pulse train, an optical delay of 1 ns is required, and toenable the 100^(th) pulse in the train to coincide with the input pulsefrom the 10 MHz source, the optical delay might have to be preciselycontrolled. The optical delay loop includes optical gain 3120 tocompensate for signal attenuation, dispersion compensation 3160 torestore pulse-width and active optical delay control 3150. Once thepulse multiplication has occurred, the output pulse train isOOK-modulated 3175 with a data stream 3182 to generated RZ signal 3190,and amplified in an erbium-doped fiber amplifier 3185 to bring the pulseenergy up to the same level as that of the input pulse train (or up tothe desired output pulse energy level).

One or more of the features described herein, whether taken alone or incombination, can be included in various aspects or implementations ofthe current subject matter. For example, in some aspects, an opticalwireless communication system can include at least one USPL lasersource, which can optionally include one or more of pico-second,nano-second, femto-second and atto-second type laser sources. An opticalwireless communication system can include USPL sources that can befiber-coupled or free-space coupled to an optical transport system, canbe modulated using one or more modulation techniques forpoint-to-multi-point communications system architectures, and/or canutilize optical transport terminals or telescopes manufactured throughone or more of hyperbolic mirror fabrication techniques, conventionalNewtonian mirror fabrication techniques, or other techniques that arefunctionally equivalent or similar. Aspheric aspheric optical designscan also or alternatively be used to minimize, reduce, etc. obscurationof a received optical signal.

Free-space optical transport systems consistent with implementations ofthe current subject matter can utilize USPL laser designs that focus areceived signal at one ideal point. In some implementations onetelescope or other optical element for focusing and delivering light canbe considered as a transmitting element and a second telescope or otheroptical element for focusing and receiving light positioned remotelyfrom the first telescope or other optical element can function as areceiving element to create an optical data-link. Both opticalcommunication platforms can optionally include components necessary toprovide both transmit and receive functions, and can be referred to asUSPL optical transceivers. Either or both of the telescopes or otheroptical elements for focusing and delivering light can be coupled to atransmitting USPL source through either via optical fiber or by afree-space coupling to the transmitting element. Either or both of thetelescopes or other optical elements for focusing and receiving lightcan be coupled to a receive endpoint through either optical fiber or afree-space coupling to the optical receiver. A free-space optical (FSO)wireless communication system including one or more USPL sources can beused: within the framework of an optical communications network, inconjunction with the fiber-optic backhaul network (and can be usedtransparently within optical communications networks within an opticalcommunications network (and can be modulated using On-Off keying (OOK)Non-Return-to-Zero (NRZ), and Return-to-Zero (RZ) modulation techniques,within the 1550 nm optical communications band), within an opticalcommunications network (and can be modulated usingDifferential-Phase-Shift Keying (DPSK) modulation techniques), within anoptical communications network (and can be modulated using commonly usedmodulation techniques for point-to-point communications systemarchitectures using commonly used free-space optical transceiverterminals), within an optical communications network utilizing D-TEKdetection techniques, within a communications network for use inconjunction with Erbium-Doped Fiber Amplifiers (EDFA) as well as highpower Erbium-Ytterbium Doped Fiber Amplifiers (Er/Yb-DFA), within anoptical communications network (and can be modulated using commonly usedmodulation techniques for point-to-multi-point communications systemarchitectures), etc.

USPL technology can, in some aspects, be utilized as a beacon source toproviding optical tracking and beam steering for use in auto-trackingcapabilities and for maintaining terminal co-alignment during operation.The recovered clock and data extracted at the receive terminal can beused for multi-hop spans for use in extending network reach. The opticalnetwork can be provided with similar benefits in WDM configurations,thereby increasing the magnitude of effective optical bandwidth of thecarrier data link. USP laser sources can also or alternatively bepolarization multiplexed onto the transmitted optical signal to providepolarization multiplex USP-FSO (PM-USP-FSO) functionality. The recoveredclock and data extracted at the receive terminal can be used formulti-hop spans for use in extending network reach, and can include ageneric, large bandwidth range of operation for providing data-rateinvariant operation. An optical pre-amplifier or semi-conductor opticalamplifier (SOA) can be used prior to the optical receiver element and,alternatively or in combination with the recovered clock and dataextracted at the receive terminal, can be used for multi-hop spans foruse in extending network reach, having a generic, large bandwidth rangeof operation for providing data-rate invariant operation. Terminalco-alignment can be maintained during operation, such that significantimprovement in performance and terminal co-alignment can be realizedthrough the use of USPL technology, through the use of USPL data sourceas well as providing a improved approach to maintaining transceiveralignment through the use of USPL laser beacons.

USPL-FSO transceivers can be utilized in some aspects for performingremote-sensing and detection for signatures of airborne elements usingionization or non-ionization detection techniques, utilizing opticaltransport terminals manufactured through either the Hyperbolic MirrorFabrication Techniques or conventional Newtonian designs that focus areceived signal at one ideal point. USPL-FSO transceivers consistentwith implementations of the current subject matter can be utilized innon-line of sight lasercom applications. USPL-FSO transceiversconsistent with implementations of the current subject matter can allowadjustment of the distance at which the scattering effect (enabling NLOStechnique) takes place, reception techniques to improve detectionsensitivity using DTech detection schemes, and improved bandwidth viabroadband detectors including frequency combs. USPL-FSO transceiversconsistent with implementations of the current subject matter can beutilized in conjunction with Adaptive Optic (AO) Techniques forperforming incoming optical wave-front correction (AO-USPL-FSO).USPL-FSO transceivers consistent with implementations of the currentsubject matter can be utilized and operate across the 1.3 to 1.6 micronwavelength range. USPL-FSO transceivers consistent with implementationsof the current subject matter can be utilized in conjunction withoptical add-drop and optical multiplexing techniques, in bothsingle-mode as well as multi-mode fiber configurations. A USPL-FSOtransceiver consistent with implementations of the current subjectmatter can be utilized and operated across the 1.3 to 1.6 micronwavelength range as a range-finder and spotting apparatus for thepurposes of target identification and interrogation applications.

In other aspects of the current subject matter, a series of switchednetwork connections, such as for example 10 GigE, 100 GigE, or the likeconnections can be connected from one point to another, either overfiber or free-space optics, for example via Time Division Multiplexing(TDM).

A mode-locked USPL source consistent with implementations of the currentsubject matter can be used to generate both clock and data streams.Mode-locked lasers can represent a choice of a high performance, highfinesse source for clocks in digital communication systems. In thisrespect, mode-locked fiber lasers—in either linear or ringconfiguration—can make an attractive candidate of choice, as they canachieve pulse widths of the USPL sources region and repetition rate ashigh as GHz.

High harmonic generation can be achieved using carbon nano-tubessaturable absorbers. Passive mode-locked fiber lasers using carbonnano-tubes saturable absorbers (CNT-SA) make an option for high rep ratesources due to their ability to readily generate high harmonics of thefundamental rep rate.

FSO can be used in terrestrial, space and undersea applications.

Conditional path lengths control from splitter to aperture can be animportant parameter. TDM multiplexes can be employed consistent withimplementations of the current subject matter to control the relativetemporal time delay between aperture-to-source paths. Each pulse traincan be controlled using parallel time delay channels. This technique canbe used to control conventional multiple-transmit FSO aperture systemsemploying WDM as well as TDM systems. USPL laser pulse-to-pulse spacingcan be maintained and controlled to precise temporal requirements forboth TDM and WDM systems. The techniques described can be used in TDMand WDM fiber based system. The use of TDM multiplexers as describedherein can be used implement unique encryption means onto thetransmitted optical signal. A complementary TDM multiplexer can beutilized to invert the incoming received signal, and thereby recover theunique signature of the pulse signals. A TDM multiplexer describedherein can be utilized to control WDM pulse character for the purpose ofWDM encryption. A TDM multiplexer can be used in conventional FSOsystems wherein multiple apertures connected to a common source signalare capable of having the temporal delay between pulses controlled tomaintain constant path lengths. A TDM multiplexer can be used for TDMfiber based and FSO based systems. A TDM multiplexer can be an enablingtechnology to control optical pulse train relationship for USPL sources.A TDM multiplexer can be used as an atmospheric link characterizationutility across an optical link through measurement of neural correctionfactor to get same pulse relational ship.

Any combination of PZ discs can be used in a transmitter and can have aninfinite number of encryption combinations for USPL based systems, bothfiber and FSO based. The timing can run from 10 GigE switches or theequivalent and to build up the USPL to a Terabit/second (or faster) ratewith a Multiplier Photonic chip, and this Terabit/second signal can bemodulated directly from the 10 GigE switch. While operating in a WDMconfiguration, an interface either to a fiber based system or to a FSOnetwork element can be included.

A system can accept an ultrafast optical pulse train and can generate atrain of optical pulses with pulse-width, spectral content, chirpcharacteristics identical to that of the input optical pulse, and with apulse repetition rate being an integral multiple of that of the inputpulse. This can be accomplished by tapping a fraction of the input pulsepower in a 2×2 optical coupler with an actively controllable opticalcoupling coefficient, re-circulating this tapped pulse over one roundtrip in an optical delay line provided with optical amplification,optical isolation, optical delay (path length) control, optical phaseand amplitude modulation, and compensation of temporal and spectralevolution experienced by the optical pulse in the optical delay line forthe purpose of minimizing temporal pulse width at the output of thedevice, and recombining this power with the 2×2 optical coupler.

Passive or active optical delay control can be used, as can optical gainutilizing rare-earth-doped optical fiber and/or rare-earth-dopedintegrated optical device and/or electrically- or optically-pumpedsemiconductor optical amplification. Dispersion compensation can beprovided using fiber-Bragg gratings and/or volume Bragg gratings.Wavelength division multiplexing data modulation of the pulse traversingthe delay line can be sued as can pulse code data modulation of thepulse traversing the delay line.

The tailoring of conventional USPL sources through synthesis of USPLsquare wave pulses can be accomplished utilizing micro-lithographicamplitude and phase mask technologies, for FSO applications. The abilityto adjust pulse widths using technology and similar approaches tocontrol and actively control pulse with this technology can improvepropagation efficiency through FSO transmission links, thereby improvingsystem availability and received optical power levels.

Active programmable pulse shapers can be used to actively control USPLpulse-width can include matching real-time atmospheric conditions tomaximize propagation through changing environments. One or more of thefollowing techniques can be used in FSO applications to adapt theoptical temporal spectrum using techniques: Fourier Transform Pulseshaping, Liquid Crystal Modular (LCM) Arrays, Liquid Crystal on Silicon(LCOS) Technology, Programmable Pulse Shaping using Acousto-opticmodulators (AOM), Acousto-optic Programmable Dispersive Filter (AOPDF),and Polarization Pulse Shaping.

FIG. 32 shows a process flow chart 3200 illustrating features of amethod, one or more of which can appear in implementations of thecurrent subject matter. At 3202, a beam of light pulses each having aduration of approximately 1 nanosecond or shorter is generated. At 3204,a modulation signal is applied to the beam to generate a modulatedoptical signal. The modulation signal carrying data for transmission toa remote receiving apparatus. The modulated optical signal is receivedat an optical transceiver within an optical communication platform at3206, and at 3210 the modulated optical signal is transmitted using theoptical transceiver for receipt by the second optical communicationapparatus

FIG. 33 shows another process flow chart 3300 illustrating features of amethod, one or more of which can appear in implementations of thecurrent subject matter. At 3302, a beam of light pulses each having aduration of approximately 1 nanosecond or shorter is generated, forexample using a USPL source. The beam of light pulses is transmitted at3304 toward a target atmospheric region via an optical transceiver. At3306, optical information received at the optical transceiver as aresult of optical backscattering of the beam of light pulses from one ormore objects in the target atmospheric region is analyzed.

FIG. 34 shows another process flow chart 3400 illustrating features of amethod, one or more of which can appear in implementations of thecurrent subject matter. At 3402, first and second beams comprising lightpulses are generated, for example by a USPL source. At 3404, a firstmodulation signal is applied to the first beam to generate a firstmodulated optical signal and a second modulation signal is applied tothe second beam to generate a second modulated optical signal. A firstpolarization state of the first modulated optical signal is adjusted at3406. Optionally, a second polarization states of the second odulatedoptical signal can also be adjusted. At 3410, the first modulatedoptical signal having the adjusted first polarization state ismultiplexed with the second modulated signal. At 3412, the multiplexedfirst modulated optical signal having the adjusted first polarizationstate with the second modulated signal is transmitted by an opticaltransceiver for receipt by a second optical communication apparatus.

One or more aspects or features of the subject matter described hereincan be realized in digital electronic circuitry, integrated circuitry,specially designed application specific integrated circuits (ASICs),field programmable gate arrays (FPGAs) computer hardware, firmware,software, and/or combinations thereof. These various aspects or featurescan include implementation in one or more computer programs that areexecutable and/or interpretable on a programmable system including atleast one programmable processor, which can be special or generalpurpose, coupled to receive data and instructions from, and to transmitdata and instructions to, a storage system, at least one input device,and at least one output device.

These computer programs, which can also be referred to as programs,software, software applications, applications, components, or code,include machine instructions for a programmable processor, and can beimplemented in a high-level procedural and/or object-orientedprogramming language, and/or in assembly/machine language. As usedherein, the term “machine-readable medium” refers to any computerprogram product, apparatus and/or device, such as for example magneticdiscs, optical disks, memory, and Programmable Logic Devices (PLDs),used to provide machine instructions and/or data to a programmableprocessor, including a machine-readable medium that receives machineinstructions as a machine-readable signal. The term “machine-readablesignal” refers to any signal used to provide machine instructions and/ordata to a programmable processor. The machine-readable medium can storesuch machine instructions non-transitorily, such as for example as woulda non-transient solid-state memory or a magnetic hard drive or anyequivalent storage medium. The machine-readable medium can alternativelyor additionally store such machine instructions in a transient manner,such as for example as would a processor cache or other random accessmemory associated with one or more physical processor cores.

To provide for interaction with a user, one or more aspects or featuresof the subject matter described herein can be implemented on a computerhaving a display device, such as for example a cathode ray tube (CRT) ora liquid crystal display (LCD) or a light emitting diode (LED) monitorfor displaying information to the user and a keyboard and a pointingdevice, such as for example a mouse or a trackball, by which the usermay provide input to the computer. Other kinds of devices can be used toprovide for interaction with a user as well. For example, feedbackprovided to the user can be any form of sensory feedback, such as forexample visual feedback, auditory feedback, or tactile feedback; andinput from the user may be received in any form, including, but notlimited to, acoustic, speech, or tactile input. Other possible inputdevices include, but are not limited to, touch screens or othertouch-sensitive devices such as single or multi-point resistive orcapacitive trackpads, voice recognition hardware and software, opticalscanners, optical pointers, digital image capture devices and associatedinterpretation software, and the like. A computer remote from ananalyzer can be linked to the analyzer over a wired or wireless networkto enable data exchange between the analyzer and the remote computer(e.g. receiving data at the remote computer from the analyzer andtransmitting information such as calibration data, operating parameters,software upgrades or updates, and the like) as well as remote control,diagnostics, etc. of the analyzer.

The subject matter described herein can be embodied in systems,apparatus, methods, and/or articles depending on the desiredconfiguration. The implementations set forth in the foregoingdescription do not represent all implementations consistent with thesubject matter described herein. Instead, they are merely some examplesconsistent with aspects related to the described subject matter.Although a few variations have been described in detail above, othermodifications or additions are possible. In particular, further featuresand/or variations can be provided in addition to those set forth herein.For example, the implementations described above can be directed tovarious combinations and subcombinations of the disclosed featuresand/or combinations and subcombinations of several further featuresdisclosed above. In addition, the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. Other implementations may be within the scope of the followingclaims.

What is claimed is:
 1. An optical communication apparatus comprising: anultra-short-pulse-laser (USPL) source that generates a beam comprisinglight pulses each having a duration of approximately 1 nanosecond orshorter; a modulation element that applies a modulation signal to thebeam generated by the USPL source to generate a modulated opticalsignal, the modulation signal carrying data for transmission to a secondoptical communication apparatus; an optical transceiver that receivesthe modulated optical signal and transmits the modulated optical signalfor receipt by the second optical communication apparatus; and whereinthe optical transceiver is configured to detect atmospheric elementsenabling analysis of a backscattered signal of an air-borne particulatesignature of the detected atmospheric elements to enable adjustment ofthe beam generated by the USPL source enhancing atmospheric penetration.2. An optical communication apparatus as in claim 1, wherein themodulation element comprises at least one of a direct modulationelement, an indirect modulation element, and an external modulationelement, the external modulation element being external to the USPLsource.
 3. An optical communication apparatus as in claim 1, wherein theduration is less than approximately a picosecond.
 4. An opticalcommunication apparatus as in claim 1, wherein the duration is less thanapproximately a femtosecond.
 5. An optical communication apparatus as inclaim 1, wherein the duration is less than approximately an attosecond.6. An optical communication apparatus as in claim 1, further comprisingan optical multiplexer that multiplexes more than one communicationchannel into the beam.
 7. An optical communication apparatus as in claim1, further comprising an optical amplifier disposed between the USPLsource and the optical transceiver, the optical amplifier increasing anoutput power of the modulated optical signal transmitted by the opticaltransceiver.
 8. An optical communication apparatus as in claim 7,wherein the optical amplifier comprises at least one of an opticalpre-amplifier, a semi-conductor optical amplifier, an erbium-doped fiberamplifiers, and an erbium-ytterbium doped fiber amplifier.
 9. An opticalcommunication apparatus as in claim 1, further comprising a second USPLsource supplying a second beam of light pulses to the opticaltransceiver, the second USPL source serving as a tracking and alignmentbeacon to determine or verify a target point for the transmittedmodulated optical signal at the remote receiving apparatus.
 10. Anoptical communication apparatus as in claim 1, wherein a tracking andalignment beacon signal is generated within the modulated opticalsignal, the tracking and alignment beacon signal being used to determineor verify a target point for the transmitted modulated optical signal atthe remote receiving apparatus.
 11. An optical communication apparatusas in claim 1, further comprising a polarization dependent multiplexercomponent that multiplexes optical signals of differing polarity beforetransmission of the modulated optical signal to the second opticalcommunication apparatus.
 12. An optical communication apparatus as inclaim 1, further comprising a polarization dependent de-multiplexercomponent that de-multiplexes optical signals of differing polarityreceived as a second modulated optical signal from the second opticalcommunication apparatus.
 13. An optical communication apparatus as inclaim 12, wherein the de-multiplexed optical signals are each interfacedto a different optical network for network usage.
 14. An opticalcommunication apparatus as in claim 1, wherein the detected atmosphericelements further comprise aerosols, fog and scintillation effects.
 15. Amethod of optical communication comprising: generating by anultra-short-pulse-laser (USPL) source a beam comprising light pulseseach having a duration of approximately 1 nanosecond or shorter;applying by a modulation element a modulation signal to the beam togenerate a modulated optical signal, the modulation signal carrying datafor transmission to a remote receiving apparatus; receiving themodulated optical signal at an optical transceiver; transmitting, usingthe optical transceiver, the modulated optical signal for receipt by thesecond optical communication apparatus; and detecting by the opticaltransceiver atmospheric elements enabling analysis of a backscatteredsignal of an air-borne particulate signature of the detected atmosphericelements to enable adjustment of the beam enhancing atmosphericpenetration.
 16. A method as in claim 15, wherein the generating isperformed by an ultra-short-pulse-laser (USPL) source.
 17. A method asin claim 15, wherein the applying is performed by a modulation element,the modulation element comprising at least one of a direct modulationelement, an indirect modulation element, and an external modulationelement, the external modulation element being external to the USPLsource.
 18. An optical communication apparatus as in claim 15, whereinthe detected atmospheric elements further comprise aerosols, fog andscintillation effects.
 19. A remote sensing apparatus comprising: anultra-short-pulse-laser (USPL) source that generates a beam comprisinglight pulses each having a duration of approximately 1 nanosecond orshorter; an optical transceiver that transmits the beam of light pulsestoward a target atmospheric region; and detection circuitry foranalyzing optical information received at the remote sensing apparatusas a result of optical backscattering from one or more objects in thetarget atmospheric region, wherein the detection circuitry is configuredto analyze a backscattered signal of an air-borne particulate signatureof the one or more objects in the target atmospheric region enablingadjustment of the beam generated by the USPL source enhancingatmospheric penetration of the beam generated by the USPL source.
 20. Aremote sensing apparatus as in claim 19, further comprising aspectrographic analysis component for analyzing spectroscopicinformation extracted from the optical information received at theremote sensing apparatus.
 21. An optical communication apparatus as inclaim 19, wherein the optical information further comprises aerosols,fog and scintillation effects.
 22. A method of remote sensingcomprising: generating, using a USPL source, a beam of light pulses eachhaving a duration of approximately 1 nanosecond or shorter; transmittingthe beam of light pulses toward a target atmospheric region via anoptical transceiver; analyzing optical information received at theoptical transceiver as a result of optical backscattering of the beam oflight pulses from one or more objects in the target atmospheric regionincluding a backscattered signal of an air-borne particulate signatureto enable adjustment of the beam generated by the USPL source; andadjusting the beam generated by the USPL source based on the analyzedoptical information enhancing atmospheric penetration of the beamgenerated by the USPL source.
 23. An optical communication apparatus asin claim 22, wherein the optical information further comprises aerosols,fog and scintillation effects.
 24. An optical communication apparatuscomprising: a first laser source that generates a first beam comprisinglight pulses; a second laser source that generate a second beamcomprising light pulses a first modulation element that applies a firstmodulation signal to the first beam to generate a first modulatedoptical signal, the first modulation signal carrying first data fortransmission to a remote optical communication apparatus; a secondmodulation element that applies a second modulation signal to the secondbeam to generate a second modulated optical signal, the secondmodulation signal carrying second data for transmission to the remoteoptical communication apparatus; a first polarization component thatadjusts a first polarization state of the first modulated opticalsignal; a polarization dependent multiplexer component that multiplexesthe first modulated optical signal having the adjusted firstpolarization state with the second modulated signal; and an opticaltransceiver that receives the multiplexed optical signal first modulatedoptical signal with the adjusted first polarization state with thesecond modulated signal transmits the multiplexed first modulatedoptical signal having the adjusted first polarization state with thesecond modulated signal for receipt by the second optical communicationapparatus; and wherein the optical transceiver is configured to detectatmospheric elements enabling analysis of a backscattered signal of anair-borne particulate signature of the detected atmospheric elements toenable adjustment of the first and second beam generated by the firstand second laser source enhancing atmospheric penetration.
 25. Anoptical communication apparatus as in claim 24, wherein the detectedatmospheric elements further comprise aerosols, fog and scintillationeffects.